PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003 
ICS 27.160.20 
 
© EAC 2008 First Edition 2008 
 
 
 
 
   
 
 
EAST AFRICAN STANDARD 
 
Batteries for use in photovoltaic power systems — Specification —  
 
Part 1: 
General requirements  
 
 
  
 
 
PUBLIC REVIEW DRA FT, SEPTEMBER 2008  
 
 
  
 
  
 
   
 
 
 
EAST AFRICAN COMMUNITY  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
ii © EAC 2008 — All rights reserved  
 
Foreword 
 
Development of the East African Standards ha s been necessitated by the need for harmonizing 
requirements governing quality of products and serv ices in East Africa. It is envisaged that through 
harmonized standardization, trade barriers which are encountered when goods and services are 
exchanged within the Comm unity will be removed.  
 
In order to meet the above objectives, the EAC Partner States have enacted an East African 
Standardization, Quality Assurance, Metrology an d Test Act, 2006 (EAC SQMT Act, 2006) to make 
provisions for ensuring standardization, quality as surance, metrology and testing of products 
produced or originating in a third country and traded in  the Community in order to facilitate industrial 
development and trade as well as helping to protect the health and safety of society and the 
environment in the Community. 
 East African Standards are formulat ed in accordance with the proc edures established by the East 
African Standards Committee. The East Afri can Standards Committee is established under the 
provisions of Article 4 of the EAC SQMT Act, 2006. The Committee is composed of representatives of the National Standards Bodies in Partner States, t ogether with the representatives from the private 
sectors and consumer organizations. Draft East African Standards are circ ulated to stakeholders 
through the National Standards Bodies in the Pa rtner States. The comments received are discussed 
and incorporated before finalization of standards, in accordance with the procedures of the 
Community.   Article 15(1) of the EAC SQMT Act, 2006 provides t hat “Within six months of the declaration of an 
East African Standard, the Partner States shall adopt, without deviation from the approved text of the 
standard, the East African Standard as a nationa l standard and withdraw any existing national 
standard with similar scope and purpose”. 
 
East African Standards are subject to review, to keep  pace with technological advances. Users of the 
East African Standards are therefore expected to ensure that they  always have the latest versions of 
the standards they are implementing.  
 
© East African Community 2008 — All rights reserved
* 
East African Community  
P O Box 1096  
Arusha  
Tanzania  Tel: 255 27 2504253/8 
Fax: 255-27-2504481/2504255 
E-Mail: eac@eachq.org
 
Web: www.each.int 
                                                 
* © 2008 EAC — All rights of exploitation in any form and by an y means reserved worldwide for EAC Partner States’ NSBs.  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved iii  
Introduction 
 
The PV system designer depends on the capacity of  a storage battery for reliable extended operation 
of the system load during hours of  darkness and below-average solar resource. Photovoltaic systems 
can subject batteries to harsh operational environme nts with minimal control of recharge profiles. The 
economics of photovoltaic modules limit the ability to  charge the battery at more traditional motive 
power deep cycle charge rates and times. Typical ch arge rates for small PV systems are less than 6.5 
amperes and may be less than 2.0 amperes per 100 am pere-hours of battery capacity. Relatively low 
rates, coupled with the unpredictability of the sola r resource, results in limited recharge capabilities. 
 
Standalone PV systems are typically used in remote locations with minimal power resources, which 
limits the amount of initial battery boost charging po ssible. In daily operation, the limited available PV 
charging source combined with relatively low-char ge regulation voltages may be insufficient to provide 
a full charge to the battery. In an effort to i dentify appropriate standalone PV system parameters 
together with appropriate battery technology, repeat able test procedures are provided to verify PV 
system parameters. This test procedure is designed  to be characteristic of the low-charge/discharge 
rates, shallow cycle operation, and variou s charging methods used in PV systems. 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
iv © EAC 2008 — All rights reserved  
Contents 
 
1 Scope ....................................................................................................................... .................. 1 
2 Normative re ferences ........................................................................................................ ......... 1 
3 Defini tions ................................................................................................................. ................. 2 
4 Conditions of use ........................................................................................................... ............ 4 
4.1 Photovolta ic system ....................................................................................................... ............ 4 
4.2 Secondary cells  and batte ries ............................................................................................. ....... 4 
4.3 General operat ing conditions .............................................................................................. ....... 5 
5 General r equireme nts ........................................................................................................ ........ 8 
5.1 General ................................................................................................................... ................... 8 
5.2 Mechanical endurance ...................................................................................................... ....... 10 
5.3 Marking ................................................................................................................... ................. 10 
6 Functional characteristics and specific requi rements .............................................................. 10 
6.1 Capacity .................................................................................................................. ................. 10 
6.2 Cycle life ................................................................................................................ ................... 11 
6.3 Charge-disch arge efficiency ............................................................................................... ..... 12 
6.4 Resistance to overcharge .................................................................................................. ...... 12 
6.5 Charge re tention .......................................................................................................... ............ 12 
6.6 Charge acceptance afte r deep dischar ge ................................................................................ 12 
6.7 Short-circuit current and internal resistance ............................................................................ 12 
6.8 Mechanical endurance ...................................................................................................... ....... 13 
6.9 Maximum permi ssible current ............................................................................................... ... 13 
7 Test c onditions ............................................................................................................. ............ 13 
7.1 Sampling and preparation of  batteries for testing .................................................................... 13 
7.2 Accuracy of meas uring instruments .........................................................................................  15 
7.3 Physical examination ...................................................................................................... ......... 15 
8 Test methods ................................................................................................................ ........... 16 
8.1 Verification of rated capacity  (20-hour discha rge rate) ............................................................ 16 
8.2 Cycle life ................................................................................................................ ................... 17 
8.3 Charge retention test ................................................................................................................ 18 
8.4 Cycle endurance te st in photovoltaic applicatio n (extreme conditions) ................................... 18 
8.5 Charge acceptance afte r deep dischar ge ................................................................................ 20 
8.6 Short-circuit current and inter nal resistance deter mination ..................................................... 20 
8.7 Mechanical endur ance tests — Ther mal cycling ..................................................................... 22 
8.8 Mechanical endurance te sts — Bump test .............................................................................. 22 
8.9 Mechanical e ndurance tests — Drop test ................................................................................ 22 
8.10 Mechanical endur ance tests — Vibr ation test ......................................................................... 23 
8.11 High rate disc harge capabi lity ........................................................................................... ....... 23 
8.12 Overcharge resist ance test method ........................................................................................ . 23 
8.13 Content and durability of  required ma rkings ............................................................................ 2 4 
9 Guarant ee ................................................................................................................... ............. 25 
10 Marking .................................................................................................................... ................ 25 
10.1 Marking on  battery ....................................................................................................... ............ 25 
10.2 Information to be su pplied on the package .............................................................................. 2 5 
10.3 Marking of  polarity ...................................................................................................... .............. 26 
11 Recommended use of tests ................................................................................................... .. 26 
11.1 Type test ................................................................................................................ .................. 26 
11.2 Acceptance test ........................................................................................................................ 27 
12 Safety ..................................................................................................................... .................. 27 
13 Documentation .............................................................................................................. ........... 27 
Annex A (informative)  Ten-hour rate capacity (10 hour disc harge rate) .............................................. 28 
Annex B (informative)  Lead- acid battery technologi es ........................................................................ 29 
Annex C (informative)  Lead-ac id battery char acterist ics ..................................................................... 32 
Annex D (informative)  PV system  operational par ameters .................................................................. 37 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  1  
Batteries for use in photovoltaic power systems — Specification — 
Part 1: General requirements 
  
1 Scope 
 
This East African Standard specifies general requ irements and methods of test for secondary cells 
and batteries used in photovoltaic power systems.  
This East African Standard does not include specific information relating to battery sizing, method of 
charge or PV system design. 
 
This standard provides guidance in understanding  battery charging requirements in relation to the 
operational parameters that affect overall PV system  design and battery performance. This standard 
will aid in battery selection, evaluation, and PV sy stem design, and provides methods of test for 
evaluating the selected battery.  
NOTE This standard is applicable to lead- acid and nickel-cadmium cells and batteries . It is intended to amend this standard 
to include other electrochemical sy stems when they become available.  
 
2 Normative references 
 
The following referenced documents are indispensabl e for the application of this standard. For dated 
references, only the edition cited applies. For undated  references, the latest edition of the referenced 
document (including any amendments) applies.  
IEC 60050-482, International Electrotechnical Vocabulary (IEV) — Part 482: Primary and secondary 
cells and batteries 
 
IEC 60622, Secondary cells and batteries containing alkaline or other non-acid electrolytes 
— Sealed 
nickel-cadmium prismatic rechargeable single cells 
 
IEC 60623, Secondary cells and batteries containing alkaline or other non-acid electrolytes — Vented 
nickel-cadmium prismatic rechargeable single cells 
 
IEC 60721-1, Classification of environmental conditions — Part 1: Environmental parameters and 
their severities 
 
IEC 60896-11, Stationary lead-acid batteries — Part 11:  Vented types — General requirements and 
methods of test 
 
IEC 60896-21, Stationary lead-acid batteries — Part 21: Valve-regulated types — Methods of test 
 IEC 61056-1, General purpose lead-acid batteries (valve-regulated types) — Part 1: General 
requirements, functional charac teristics — Methods of test 
 
IEC 62259, Secondary cells and batteries containing alkalin e or other non-acid electrolytes — Nickel 
cadmium prismatic secondary single cells with partial gas recombination  
 
CD/K/04-2:2003, Batteries for use in photovoltaic power sy stems — Specification — Part 2: Modified 
lead acid batteries  
EAS 121, Water for lead acid batteries — Specification  
 EAS 362, Solar photovoltaic power systems — Glossary  
 
KS 1783, Rubber and plastic containers for lead-acid storage batteries — Specification EAST AFRICAN STANDARD PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
2 © EAC 2008 — All rights reserved  
KS 242, Specification for sulfuric acid for use in lead-acid batteries  
 
EAS 122, Sulfuric acid — Specification  
 
IEC 60254-1, Lead-acid traction batteries — Part 1: G eneral requirements and methods of tests  
 
3 Definitions 
 
For purposes of this East African Standard, the de finitions and terms for secondary cells and batteries 
given in IEC 60050-482, and thos e for photovoltaic generator system s given in EAS 362 in addition to 
those given below apply.   
 
3.1 
ampere-hour a unit of measure for battery capacity, obtained by mu ltiplying the current flow in amperes by the time 
in hours during which the current flows 
 
3.2 
ampere-hour capacity 
the number of ampere-hours which a cell or battery  can deliver under specified conditions, i.e. 
charging conditions, the rate of discharge, temperature and final voltage 
 
3.3 ampere-hours (Ah) charge efficiency 
ratio of the Ah discharged by the required Ah ch arged to maintain battery capacity under specific 
cycle and charging conditions 
 
3.4 
battery two or more cells electrically connected, generally in series to meet the required voltage and ampere-
hour capacity 
 
3.5 
battery capacity the total number of ampere-hours that can be withdr awn from a fully charged battery at a given rate of 
discharge to a specified cut-off voltage 
 
3.6 
battery electrolyte 
a conducting medium in the battery cell in which the flow of  electric current takes place by the 
migration of ions 
 3.7 C
20 
the rated capacity of a battery sp ecified at a constant discharge curre nt which will fully discharge the 
battery in 20 h 
 
3.8 
cell 
the smallest functional unit of a battery 
 
3.9 calculated photovoltaic (PV) array amphe re-hours (Ah) to load Ah ratio (A:L) 
The monthly daily average PV ampere-hours avail able divided by the monthly daily average load 
ampere-hours. Average daily PV ampere-hours are calculated by taking the daily average solar 
resource for each month in kWh/m
2 times the PV array current at its maximum power point (Imp) at 
standard test conditions (STC). Array to load ratios can also be calculated in terms of their respective 
Watt-hour parameters. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  3  
3.10 
Charge ampere-hours (Ah) to load Ah ratio (C:L) The total available charge ampere-hours (Ah) divide d by the load Ah. Charge Ah are calculated by 
integrating the set charge current over the total char ge time. The actual charge Ah is not necessarily 
the calculated charge Ah because of char ge current tapering at regulation voltage. 
 
3.11 
charge controller An electrical control device that regulates battery charging by voltage contro l and/or other means. It 
may also incorporate one or more of the following functions: discharge termination, regulation voltage temperature compensation, load control, and status indication. 
 3.12 c/x charge/discharge rate 
the manufacturer's rated battery capacity in ampere -hours usually at the 20 h rate divided by the 
discharge time in hours. A 100 Ah battery dischar ged/charged at the 35 h rate would result in a 
discharge/charge current of 2.86 ampere (100/35 = 2.86 ampere). 
 
3.13 deficit charge 
Charging a battery with less ampere-hours (Ah) than is  required to return the battery to its initial state-
of charge. This results in a reduct ion in the battery state-of charge. 
 
3.14 
end-of discharge voltage  
(EODV) 
The battery voltage just prior to load termination. It will be the minimum voltage for the given discharge cycle. 
 
3.15 
days of autonomy the number of days which a fully charged battery can support the load with no power received from 
external sources e.g. photovoltaic (PV) array 
 
3.16 
deep cycle battery a battery which is designed so that up to 80 % of the rated ampere-hours can be removed on a 
regular daily basis without damage or unduly shortening life  
3.17 
end-of-charge voltage 
the cell or battery voltage at which charging is normally terminated by the charging source or 
continued at constant voltage condition 
 3.18 lead-acid battery 
electrochemical storage device t hat includes pure lead, lead-antim ony, or lead-calcium types with 
sulphuric acid electrolyte 
 
3.19 
rated capacity the full amount of energy a battery can deliver w hen fully charged and when discharged down to a 
minimum cut-off voltage under specified conditions  of temperature, current and final voltage 
 
3.20 
terminal voltage the voltage across the terminals at any time, whethe r the battery is charging,  discharging, or in open 
circuit  PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
4 © EAC 2008 — All rights reserved 3.21 
charging and discharging efficiency test 
the efficiency test which is carried out in such a mann er that the specimen in the state of full charge is 
discharged to the cut-off voltage of discharge, char ged from this state by an ampere-hour equal to the 
discharged ampere-hour, then discharged again to the cut-off voltage of discharge 
 
3.22 
duty cycle 
Sequence of operating conditions to which a cell or batte ry is subjected. This includes factors such as 
charge and discharge rates and conditions, depth of discharge, numbers and types of cycles, 
temperatures and length of time in open circuit stand. 
 
3.23 
depth of discharge percentage of rated capacity discharged from a battery  
 
4 Conditions of use 
 
This clause identifies the operating conditions expe rienced by secondary batteries in photovoltaic 
applications during their use.  
 
4.1 Photovoltaic system 
 The photovoltaic systems with batteries referred to in this standard can supply constant, variable or 
intermittent energy to the connected equipment (load). This system may include hybrid or grid-
connected systems. The connected equipment may be pumps, refrigerators, lighting systems, 
communication systems, etc. 
 
4.2 Secondary cells and batteries 
 
4.2.1 Secondary cells and batteries used in photovoltaic systems are categorized as follows: 
 
• vented (flooded); 
 
• valve-regulated (gelled and AGM); and 
 • gas-tight sealed (nickel-cadmium only). 
 
The cells and batteries shall be delivered in any one of the following conditions:  
• discharged and drained (nickel-cadmium batteries only); 
 
• charged and filled; 
 
• dry charged and unfilled (lead-acid batteries only); and 
 
• discharged and filled (nickel-cadmium batteries only). 
 
4.2.2 Secondary cells and batteries shall meet the following requirements: 
 
a) Shall be of a design offering deep cycle capability. 
 
b) Shall have a low or no-maintenance requiremen t. Maintenance intervals in the low maintenance 
category shall be not less than four months in mean daily average temperatures of 25 °C and 
three months in mean daily temperatures of 35 °C provided that battery char ge is at the current 
rate and voltage recommended by  the manufacturer of the battery. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  5  
4.3 General operating conditions 
 
Batteries in a typical PV system operating under av erage site weather conditions may be subjected to 
the following conditions. 
 
4.3.1 Autonomy time  
 
The battery is designed to supply energy under spec ified conditions for periods of time typically 3 
days without or with minimum solar irradiation. So me systems can have signif icantly more or less 
than this time. 
 
Autonomy for a non-essential system shall be two days, and for essential systems five days at an 
average daily consumption. 
 
NOTE 1 When calculating the required battery c apacity, the following items should be considered: 
 
• required daily/seasonal cycle (there may be re strictions on the maximum depth of discharge); 
 
• time required to access the site; 
 
• ageing; 
 
• temperature impact; 
 
NOTE 2 The requirements of this clause ar e aimed at ensuring that suppliers take into account the requirements of the PV 
system that the battery is to be used. 
 
4.3.2 Typical charge and discharge currents  
 
The charge current generated by t he photovoltaic generator and the discharge current determined by 
the load are shown in Table 1. 
 
Table 1 — Charge and discharge currents 
 
 Lead acid  Nickel cadmium  
Charge current generated by the PV generator    
 Maximum charge current  I20  = C20/20h  I20  = It /20  
 Average charge current  I50 = C50/50h  I50  = It /50  
Discharge current determined by the load    
 Average discharge current  I120  = C120/120h  I120  = It /120  
NOTE 1 Depending on the system design, e.g. for hybrid syst ems, the charge and the discharge current may vary in a 
wider range.  
NOTE 2 In some systems the load current must be supplied at the same time as the battery charging current.  
NOTE 3  
For lead acid For nickel cadmium  
Cn is the rated capacity (Ah)  
n is the time base in hours for which the capacity is 
declared  Cn is the rated capacity (Ah) n is the time base in hours for 
which the capacity is declared  
t is the time in hours  t is the time in hours  
In = Cn / t  See IEC 61434 for the reference test current It  
It = Cn (Ah )/1 h and In = It /t  
 
4.3.3 Daily cycle  
 
The battery is normally exposed to a daily cycle with: PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
6 © EAC 2008 — All rights reserved  
a) charging during daylight hours; 
 
b) discharging during night-time hours. 
 A typical daily discharge can be in the range of 2 % to 20 % of the battery capacity. 
 
4.3.4 Seasonal cycle  
 
The battery may be exposed to a seasonal cycle of state of charge be cause of varying average 
charging conditions as follows: 
 
⎯ periods with low solar irradiation, for instanc e during overcast/cloudy days causing low energy 
production. The state of charge of the battery (available capacity) can go down to 20 % of the 
rated capacity (corresponding to  80 % depth of discharge (DOD)); 
 
⎯ periods with high solar irradiat ion, e.g. during hot and sunny days, which will bring the battery 
up to fully charged conditions, with the possib ility that the battery could be overcharged. 
 4.3.5 Period of high state of charge  
 
During hot and sunny periods for example, the battery  will be operated at a high state of charge 
(SOC), typically between 80 % and 100 % of rated capacity. 
 A voltage regulator system normally limits the ma ximum battery voltage during the recharge period. 
 
NOTE  In a "self-regulated" PV system, the battery voltage is not limited by a charge controller but by the characteristics of 
the PV generator. 
 
The system designer normally chooses the maximu m battery voltage with regard to the conflicting 
requirements of "recover to a maximum state of char ge (SOC)" as early as possible in the charging 
season but without substantially overcharging the battery.  
 
The overcharge increases the gas pr oduction resulting in water consum ption in vented cells. In valve-
regulated lead-acid cells, the overcharge will caus e a lesser increase of water consumption and gas 
emission but more heat generation. 
 
Typically the maximum charge voltage is 2.4 V per cell for lead-acid batteries and 1.55 V per cell for 
nickel-cadmium batteries at the reference temp erature specified by the manufacturer. Some 
regulators allow the battery voltage to exceed thes e values for a short period as an equalizing or 
boost charge. Charge voltage compensation shall be used according to the battery manufacturer instructions if the battery operat ing temperature deviates significantl y from the reference temperature. 
 The expected life-time of a battery in a PV system  even kept regularly at a high state of charge may 
be considerably less than the published life of t he battery used under continuous float charge. 
 
4.3.6 Period of sustained low state of charge  
 
During periods of low solar irradiation, the ene rgy produced by the photovoltaic array may not be 
sufficient to fully recharge the battery. The state of charge will then decrease and cycling will take 
place at a low state of charge. Th e low solar irradiation on the photovoltaic array may be a result of 
the geographical location combined with the wint er periods, heavy clouds, rains or accumulation of 
dust on photovoltaic array. 
 
4.3.7 Electrolyte stratification  
 
Electrolyte stratification may occur in lead-acid batteries. In vented lead-acid batteries, electrolyte 
stratification can be avoided by electrolyte agitation or periodic overcharge whilst in service. In valve 
regulated lead-acid (VRLA) batteries, electrolyte stratification can be avoided by design or by 
operating them according to the manufacturer’s instructions. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  7  
4.3.8 Storage  
 
Manufacturers’ recommendations for storage shall be observed. In the absence of such information, 
the storage period shall be estimated according to t he climatic conditions as shown in Table 2 as 
below.  
Table 2 — Limit values for storage conditions of  batteries for photovoltaic applications 
 
Battery type Temperature range
°C Humidity
% Storage period for batteries
With electrolyte Without electrolyte 
Lead acid -20 to +40 <90 Up to 6 months 1 – 2 years 
(dry charged) 
Nickel-cadmium 
(Pocket plate type) -20 to +50 
(standard electrolyte)  
<90  
Up to 6 months  
1 – 3 years 
(fully discharged, 
drained and sealed) -40 to +50 
(high density electrolyte) 
 
With electrolyte, a lead-acid or nickel-cadmium  battery shall be stored at full state of charge. 
 
A loss of capacity may result from exposure of a battery to high temperature and humidity during 
storage. 
 
NOTE The temperature of a battery stored in a container in direct  sunlight, can rise to 60 °C or more in daytime. Choice of a 
shaded location or cooling should avoid this risk.  
 
4.3.9 Operating temperature  
 
The temperature range during operation experienced by  the battery at the site is an important factor 
for the battery selection and the expected lifetime (see IEC 60721-1 for definitions of climatic 
conditions).  Manufacturers’ recommendations for operating temperatures and humidity shall be observed. In the 
absence of such information, operating temperatur es and humidity shall be those shown in Table 3. 
 
Table 3 — Limit values for operating conditions of batteries for photovoltaic applications 
 
Battery type  Temperature range  
°C  Humidity  
%  
Lead-acid  –15 to +40  <90  
Nickel-cadmium (standard electrolyte)  –20 to +45  <90  
Nickel-cadmium (high density electrolyte)  –40 to +45  <90  
NOTE 1 The manufacturer should be consulted for temperat ures outside this range. Typically the life expectancy of 
batteries will decrease with increasing operating temperature.  
 
NOTE 2 Low temperature will reduce the discharge performanc e and the capacity of the batteries. For details, the 
manufacturer should be consulted.  
 
4.3.10 Charge control 
 
Excessive overcharge does not increase the energy st ored in the battery. Instead, overcharge affects 
the water consumption in vented batteries and cons equently the service interval. In addition, valve-
regulated lead-acid batteries may dry out resulting in a loss of capacity and / or overheating.  
Overcharge can be controlled by use of proper charge controllers. 
 
The parameters of the regulator shall take into account the effects of the PV generator design, the 
load, the temperature and the limiting values for the battery as recommended by the manufacturer. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
8 © EAC 2008 — All rights reserved Vented lead-acid or nickel-cadmium batteries including those with partial gas recombination shall 
have sufficient electrolyte to cover at least the period between planned servic e visits. Overcharge in 
valve-regulated lead-acid batteries shall be care fully controlled to reach optimum lifetime. 
 The water consumption is measured during the cycle test (see 8.4.5) and can be used together with 
the system’s design information to estimate the service intervals. 
 
4.3.11 Physical protection  
 
Physical protection shall be provided against conse quences of adverse site conditions, for example, 
against the effects of: 
 
⎯ uneven distribution and extremes of temperature; 
 
⎯ exposure to direct sun light (UV radiation); 
 
⎯ air-borne dust or sand; 
 
⎯ explosive atmospheres; 
 
⎯ flooding, water vapor condensation and water spray; 
 
⎯ earthquakes; 
 ⎯ shock and vibration (particularly during transportation). 
 
5 General requirements 
 
5.1 General 
 
5.1.1 Construction 
 
The lead acid battery shall consist of anode plates, cathode plates, separators, containers, etc and shall be capable of serving at ambient temperatures  of -15 to +45 °C without abnormality. For sealed 
batteries with catalytic plug, however, the lower limit of ambient temperature shall be -5 °C in the monthly average. 
 
The battery shall be equipped with anode terminal and cathode terminal, and in 6 V batteries the unit 
cells shall be connected with connecting links. The surface of the electrolyte shall be monitored by 
means of the liquid surface lines (the highest and the lowest) on the si de of the container. 
 
In the vented-type battery, the clearance between the cover and container shall be sealed with a 
sealing compound so that the gas generated in the battery does not come out from parts other 
than the vent hole. The sealed type battery shall be so constructed that the gas generated from 
the battery is returned to water by the catalytic plugs or the auxiliary electrodes and almost no gas 
comes outside in normal service conditions.  
 
5.1.2 Plates 
 
In lead acid batteries active materials of the positive and negative plates (lead-dioxide and sponge 
lead, respectively in a fully charged cell) shall supp orted on lead grid structures in all but the Planté 
type cells whose plates consists of scored pure  lead sheets on which the active materials are 
produced during formation. In some cells, small amounts of antimony, along with traces of arsenic 
and other materials are often alloyed with the grid le ad to strengthen the grids, facilitate grid casting 
and increase cell life. In applications where low se lf-discharge and/or low gassing rates are important 
lead-calcium alloys or pure lead grids are sometimes used. 
 
The positive plates of a lead acid battery shall be not less than 2 mm thick. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  9 Nickel-cadmium cells are presently manufactured in  two basic types: sealed and vented. The "sealed" 
type cells also include a pressure relief vent, how ever, the vent assemblies associated with the two 
types are quite different from each other, as is t he amount of electrolyte contained within the cell. To 
some extent, performance characteristics also differ between the sealed and vented designs. In 
addition, both sealed and vented cells are availabl e with either sintered plate or pocket plate 
construction. Sintered plates are made by impregnati ng powdered active materials into sintered nickel 
support plates. With pocket designs the active materials are contained in perforated pockets formed 
into the support plates.  
 
Sintered plate cells generally have lower internal re sistance than equivalent pocket plate designs and 
are less affected by high rate or low temperature operation. However, pocket plate cells are more 
rugged and generally have longer lives.  5.1.3 Separator 
 
An effective separator shall possess a number of me chanical properties; applicable considerations 
include permeability, porosity, pore size distribution, specific su rface area, mech anical design and 
strength, electrical resistance, ionic conductivity, and chemical compatibility with the electrolyte. In 
service, the separator shall have good resistance to acid and oxidation. The area of the separator 
shall be a little larger than the area of the plates to  prevent material shorting between the plates. The 
separators shall remain stable over the operating temperature range of the battery.  5.1.4 Container 
 
Lead acid battery containers shall comply with the requirements of KS 1783. 
 
5.1.5 Explosion-proof and spray preventive device 
 The device shall maintain the function stably and not allow the elution of any harmful impurity into the 
electrolyte under normal service condition. 
 5.1.6 Sealing construction 
 The sealing construction shall function stably for a long period and not allow the elution of any 
impurity deleterious to the performance of a bat tery into the electrolyte under normal service 
condition. 
 
5.1.7 Terminals 
 The terminals shall be lug type or such that connection is made by means of bolts and nuts and not 
the tapered pillar type as normally used for starte r batteries for vehicles and shall be corrosion 
resistant, and of such a design that cleaning at intervals is easily accomplished.  
 
5.1.8 Electrolyte 
 The electrolyte for lead acid batteries shall be dilute sulphuric acid complying with KS 242 diluted with 
water conforming to EAS 121.  
The density of the electrolyte in all fully charged vented batteries shall be in the range 1.26 kg/l to 
1.30 kg/l at 25 °C unless otherwise  specified by the manufacturer. 
 
NOTE For valve-regulated batteries, the electrolyte is not accessible and, therefore, its density cannot be checked. 
 
The electrolyte for nickel-cadmium batteries is a solution of potassium hydroxide in water with 
approximately 20 to 35 percent potassi um hydroxide concentration.  
 
The electrolyte in the nickel-cadmium system acts only as an ion transport medium and is essentially 
unchanged chemically during charge or discharge. T he specific gravity of the electrolyte therefore 
remains relatively constant regardless of the state of charge of the cell.  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
10 © EAC 2008 — All rights reserved Each cell or monobloc of a battery requiring addition of  electrolyte (i.e. flooded cells) shall be provided 
with a means of indicating the highest and lowest permissible levels of electrolyte. 
 
5.2 Mechanical endurance 
 
Batteries for photovoltaic application shall be designed to withstand mechanical stresses during 
normal transportation and handling. Additional packing or protection shall be used for off-road conditions. 
 
Particular care shall be taken while handling unpack ed batteries. Manufacturer’s instructions shall be 
observed. 
 
In case of specific requirements regarding mec hanical stresses, such as earthquakes, shock and 
vibration, these shall be individually specif ied or referred to the relevant standard. 
 
5.3 Marking 
 
Any marking required by this standard shall be durabl e and legible. In considering the durability of the 
marking, the effect of normal us e shall be taken into account. 
 The durability of the marking shall be verified in accordance with 8.13.  
 
6 Functional characteristics and specific requirements 
 
6.1 Capacity 
 
6.1.1 General 
 
The main feature of a secondary cell or battery is its ability to store electr ical energy. This storage 
capacity is expressed in ampere-hours (Ah) and varies with the conditions of use (electrolyte 
temperature, discharge current and final voltage).  
To comply with this standard a battery shall be rated at the 20-hour rate of discharge (C
20) in 
accordance with 6.1.2 . A battery may also be rated at the 10-hour rate of discharge (C 10) in 
accordance with 6.1.3 . 
 
Table 4 gives typical capacity ratings of batteries used in solar applications. 
 
Table 4 — Typical capacity ratings of batteries in solar applications 
 
Capacity  
Ah Current  
A Discharge 
period  
h Final voltage  
Lead- Acid Nickel-Cadmium  
Volts per cell  Volts per cell  
C240 I 240 240 1.90 1.00 
C120 I 120 120 1.85 1.00 
C20 I 20 20 1.80 1.00 
C10 I 10 10 1.80 1.00 
C5 I 5 5 1.75 1.00 
 
6.1.2 20-hour rate 
 
The capacity of a battery at the 20-hour rate of discharge shall be determined in  accordance with 8.1. 
 When tested in accordance with 8.1, the battery s hall have a capacity of at least 90 % of the rated 
capacity on the first discharge and shall have a capaci ty equal to or greater than the rated capacity on 
or before the fifth discharge. 
 
NOTE The user should specify t he required capacity on delivery. 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  11 6.1.3 10-hour rate 
 If the battery is to be rated at the 10-hour rate, th e capacity shall be determined in accordance with 
Annex A. 
 
When tested in accordance with Annex A the battery shall have a capacity of at least: 
 
a) 85% of the rated capaci ty on the first discharge; 
 
b) 95% of the rated capacity wi thin the first five cycles; and 
 
c) 100% of the rated capacity  within the first 10 cycles. 
 
NOTE The user should specify t he required capacity on delivery. 
 
6.2 Cycle life 
 
The cycle endurance is the ability of a battery to withstand repeated charging and discharging. 
Normally the cycle endurance is given for cycles with a fixed depth of discharge and with the battery 
fully charged in each cycle. The batteries are normally  characterized by the num ber of cycles that can 
be achieved before the capacity has declined to 80 % of rated capacity as per Table 5 below.  
 
Table 5 — Cycle life and discharge characteristics of solar batteries  
 
Type of battery % depth of 
discharge % self discharge 
per month Number of 
cycles Calendar 
years life 
Lead acid 
Automotive 20 30 300 – 600 1 – 3 
 80  20  
SLI modified (vented) 20 5 – 6 1000 1 – 3 
Stationary — Vented 20 5 – 6 1000  
Stationary — Valve regulated 20 5 – 6 1200  
Valve regulated — AGM 20 2 – 3 6000 10 
 80    
Valve regulated — Gel 20 2 – 3 6500 6 – 10 
 80  2000  
Valve regulated — Tubular Gel 20 2 1200 20 
 80  3500  
Traction (motive) 80 5 – 7 1500 4 – 6 
 20 5 – 7 8000  
Tubular positive 50 1 – 3 3000 5 – 10 
 20  5000  
Low antimony 80 3 1200 3 
Sealed 20 2 – 6 400 – 1500 4 – 8 
Planté 80 2 9000 25 
Nickel Cadmium 
Pocket plates — Vented 20 2 9000 3 - 20 
 80  1000  
Pocket plates — Valve regulated 20 3 10000 20 
 80  3000  
Sintered plates — Vented 20 2 15000 8 – 20 
 80 2 3000  
Fibre Nickel Cadmium (FNC) 80 2 3000 10 
 
In photovoltaic applications the battery will be expo sed to a large number of shallow cycles but at a 
varying state of charge. The cells or  batteries shall therefore comply with the requirements of the test 
described in 8.2, which is a simulation of the PV s ystem operation. The manufacturer shall specify the 
number of cycles the cells or batteries can achiev e before the capacity has declined to 80 % of the 
rated capacity when tested in accordance with 8.2.  
 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
12 © EAC 2008 — All rights reserved 6.3 Charge-discharge efficiency 
 
6.3.1 General  
The efficiency requirement in 6.3.2 represents the ab solute coulombic efficiency at a particular state 
of charge rather than an integrated average efficien cy over a wide state of charge. This method of 
expressing efficiency is the most appropriate to the operating conditions of batteries used with photovoltaic power systems. 
 
The efficiency of batteries vary according to their depth of discharge, being relatively low for batteries having a low depth of discharge. 
 
6.3.2 Requirement 
 Where no data is available from the battery manufactu rer, batteries shall have efficiencies stated in 
Table 6. 
 
Table 6 — Battery Ah-efficiency at different states  of charge at 20 °C and a cycle depth of less 
than 20 % of the rated capacity 
 
State of charge  
(SOC)  Efficiency 
lead-acid cells  Efficiency  
nickel-cadmium cells  
90 % >85 % >80 % 
75 % >90 % >90 % 
<50 % >95 % >95 % 
 
6.4 Resistance to overcharge 
 
Batteries used in photovoltaic power systems may be subject to periods of overcharge which may 
result in loss of battery capacity. 
 When tested in accordance with 8.12, t he capacity loss shall not exceed 20 %. 
 
6.5 Charge retention 
 
The charge retention is the ability of a battery to re tain capacity during periods  of no charge, i.e. when 
not connected to a system, during transportation or  storage. A battery for solar application shall show 
a high capability of charge retention. The charge re tention shall be stated by the manufacturer but in 
no case shall the value be less than 82 %. The ab ility of a battery to retain charge shall be measured 
in accordance with 8.3. 
 
NOTE Charge retention may affect the permitted storage and autonomy time. 
 
6.6 Charge acceptance after deep discharge 
 
6.6.1 General 
 
Secondary batteries in photovoltaic systems may be  left in various states of charge for extended 
periods especially during overcast and rainy seasons. A ba ttery’s ability to recover following a period 
in partial state of discharge is impo rtant in a photovoltaic power system. 
 
6.6.2 Requirement 
 
When tested in accordance with 8.5, a battery  shall lose less than 25 % of its capacity. 
 
6.7 Short-circuit current and internal resistance  
 
This test is designed to yield values of the poss ible short circuit current (accuracy ±10 %) capable to 
be delivered from the cell and monobloc battery when the external circuit has a negligible resistance PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  13 compared to that of the unit itself. The test also yields  the values of the internal  (d.c.) resistance of the 
cell or monobloc battery when this value is derived from the voltage vs. current relationship during a 
pulsed discharge of a defined magnitude. The values of short circuit current and internal resistance 
can be used for the sizing of safety devices such as fuses. It shall be noted that the short circuit 
current of a fully discharged unit is approxima tely 60 % of that of a fully charged unit. 
 The test shall be carried out in accordance with the provisions of 8.6.  
6.8 Mechanical endurance 
 
6.8.1 When tested in accordance with 8.7, 8.8, 8.9 and 8.10, a battery shall remain leak-tight and 
shall not exhibit a change in internal resistance of more than 25 % when tested in accordance with 
8.6.  6.8.2 Vibration requirements 
 
When subjected to either the sinusoidal or random  vibration test the battery shall comply with the 
following.   a) No battery cell or component shall show di mensional distortion beyond specified limits or 
cracking of cases or covers of either cells or batteries.  
 
b) There shall be no interruption of output and no ir regular variation of voltage or current greater 
than 2 %.   
 c) There shall be no mechan ical failure of any part, electrolyte le akage or spillage of electrolyte at 
any time during the test or venting of gasse s containing entrained electrolyte (except during 
charge of vented nickel-cadmium batteries).   
 
d) The minimum value of the insulation resistance shall be 0.25 M Ω, but after cleaning and drying 
the minimum value shall be 10 M Ω. There shall be no breakdown of insulation, stripping of metal 
plating from any component part, corrosion of metal parts, or loosening of protective coating from 
the battery container or cover or deterior ation of battery identification markings.  
 
e) The battery shall comply with the rapid discharge capacity requirements. 
 
6.9 Maximum permissible current 
 
Batteries shall be suitable to maintain a current of Im = 40 × I20 for 300 s and of Ih = 200 × I20 for 5 s, 
unless otherwise specified by the m anufacturer, without distortion or other damage to the battery (see 
8.11). 
 
7 Test conditions 
 
7.1 Sampling and preparation of batteries for testing 
 7.1.1 All tests shall be carried out on new, fully char ged samples, except when the tests are used 
for re-determination of the actual capacity to assess degradation after long periods of service. 
 7.1.2 Samples shall be considered as new not later than six months after the date of manufacture. 
 
7.1.3 Batteries shall be charged at an ambient temperature of 25 °C ± 2 K 
 
⎯ either for a period of 16 h, 
 
⎯ or until the current does not change by more than 0.1 × I20 within two consecutive hours. 
 
The charge will take place either: 
 
a) from constant voltage, advised by the manufacture r, or, if not available, from the values provided 
in Table 7. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
14 © EAC 2008 — All rights reserved  
Table 7 — Default charging parameters (constant voltage/PWM) 
 
Cell Type Voltage limit 
(V per cell)a Voltage limit 
(V) a Minimum duration of constant-
voltage regulation at specific 
voltage limit (h) 
Vented, lead-antimony 2.55 15.3 3 
Vented, lead-calcium 2.66 16.0 3 
VRLA, AGM 
(see manufacturer's specifications) 2.35 14.1 12 
VRLA, gel 
(see manufacturer's specifications) 2.35 to 2.40 14.4 12 
a This value has to be within the system's operating voltage limits.  
NOTE Voltages specified for battery temperature at 25 °C + or - 3 °C. 
 
V per cell = volts per cell,  AGM = Absorbed Glass Mat, Gel = gelled electrolyte. 
 
or 
 
b) from modified constant voltage ( Uc as in a) with an initial charging current limitation of: 
 
Imax = 6 × I20. 
 
The cells or batteries are considered as fully charged when either: 
 
a) during charging at constant cu rrent, the observed voltage and elec trolyte density do not show any 
change beyond the tolerance of the measuring instru ments, during a period of 2 h, taking into 
account changes in the temperat ure of the electrolyte, or 
 
b) during charging at constant voltage, the observed current and el ectrolyte density do not show any 
change beyond the tolerance of the measuring instru ments, during a period of 2 h, taking into 
account changes in the temperature of the el ectrolyte unless other wise specified by the 
manufacturer. 
 7.1.4 Placement of batteries during testing 
 Throughout the duration of the tests, the battery sha ll be placed in a water bath at a temperature of  
25 ± 2 °C except where the test is an accelerated simula tion of a PV system. The terminal base of the 
battery shall be at least 15 mm but no more than 25 mm above the level of the water. If several 
batteries are in the same water bath, the di stance between them shall be at least 25 mm. 
 
7.1.5 Test samples shall be prepared in accordance with the following established procedures in 
the following standards: 
 
⎯ CD/04-2:2003 for modified lead acid batteries (vented types) 
 
⎯ IEC 60896-11 for stationary lead-acid batteries (vented types); 
 
⎯ IEC 60896-21 for stationary lead-acid  batteries (valve-regulated types); 
 
⎯ IEC 61056-1 for portable lead-acid batteries (valve-regulated types); 
 
⎯ IEC 60622 for sealed nickel-cadmium batteries; 
 
⎯ IEC 60623 for vented nickel-cadmium batteries; 
 
⎯ IEC 62259 for nickel cadmium prismatic rechargeable single cells with partial gas 
recombination. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  15  
⎯ IEC 60254-1 for traction lead acid batteries 
 
7.2 Accuracy of measuring instruments 
 
7.2.1 Voltage measurements 
 
The instruments used shall be of an accuracy class 0.5 or better where required. The resistance of 
the voltmeters shall be at least 10 000 Ω/V (see IEC 60051 or IEC 60485). 
 7.2.2 Current measurements 
 
The instruments used for current measurement shall be ammeters of an accuracy class equal to 0.5 
or better. The entire assembly of ammeter, shunt and leads shall be of an accuracy class of 0.5 or 
better (see IEC 60051 or refer to IEC 60359).  
7.2.3 Temperature measurement 
 
For measuring temperature, thermometers shall be used having a suitable measuring range in which 
the value of each graduated division is not in excess of 1 °C. The absolute accuracy of the 
instruments shall be at least 1 °C. 
 
NOTE As the electrolyte temperature cannot be measured directly in valve r egulated cells and monobloc batteries, an 
alternative measuring point is chosen for giving a temperature r eading as close as possible to t hat of the electrolyte. The 
preferred point of measurement is either the negative term inal or the cell wall in direct contact of the plates. 
 
7.2.4 Electrolyte density measurement  
For measuring electrolyte densities, hydrometers or other instruments shall be used with scales so 
graduated that the value of each division is not in excess of 0.005kg/l [5 kg/m
3]. The absolute 
accuracy of the instruments sha ll be at least 0.005kg/l [5 kg/m3]. 
 
7.2.5 Time measurements 
 
The time measurements shall have of an accuracy of ±0.1 % or better where required. 
 
7.2.6 Length and width measurements 
 
The instruments used shall have an accuracy  of ±0.1 % or better where required. 
 
7.2.7 Weight measurements 
 
The instruments used shall have an accuracy  of ±1 % or better where required. 
 
7.2.8 Gas volume measurements (valve regulated types) 
 
The instruments used shall have an accuracy  of ±5 % or better where required. 
 
7.2.9 Gas pressure measurements (valve regulated types) 
 
The instruments used shall have an accuracy  of ±10 % or better where required. 
 
7.3 Physical examination 
 
Prior to the commencement of the electrical and environmental testing, each battery being tested 
shall be inspected to ensure that it complies with  the requirements for PV applications as follows:   
 
a) mass and dimensions; 
 
b) minimum marking as detailed in Clause 10; 
 
c) correct warning labels;  
 
d) correct terminal connectors;  PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
16 © EAC 2008 — All rights reserved  
e) damage to case, lid and terminal connectors;  
 
f) no signs of corrosion;  
 
g) no signs of electrolyte leakage;  
 h) general standards of workmanship. 
 
8 Test methods 
 
8.1 Verification of rated capacity (20-hour discharge rate) 
 
Test samples shall be set up in accordance with th e applicable standards in 7.1.5. Tests to verify the 
rated capacity shall be performed using a current of I20 (A) for lead-acid batteries and It/5(A) for 
nickel-cadmium batteries according to the relev ant clauses in the standards listed in 7.1.5.   
 
For the capacity test using a current of I120 (A) for lead-acid batteries or It/120 for nickel-cadmium 
batteries, the discharge shall be in accordance wi th parameters stated in Table 4 and the charging 
procedure shall be carried out according to the relev ant clauses in the standar ds listed in 7.1.5   
 
8.1.1 Apparatus 
 The apparatus listed in 7.2 is required. 
 
8.1.2 Procedure 
 
The procedure shall be as follows:  
a) Prepare the battery for test in accordance with 7.1. 
 b) Monitor the temperature of one of the cells of each  battery under test, or of each cell or monobloc 
if a single cell or monobloc is being tested. The cell chosen to monitor the temperature of the battery should not be a cell at either end of the battery. 
 
c) Discharge the battery at the C
20 rate. The discharge shall commence between 1 h and 24 h after 
the battery has reached full charge, and shall be performed at a battery temperature of 25 ± 2 °C. 
The discharge current, I20, shall be held within ±2 % of the required rate. 
 
d) During the discharge, record t he following at hourly intervals: 
 
i) battery voltage;  
ii) discharge current; and  
 
iii) battery temperature. 
 e) End the discharge when the battery reaches t he final voltage specified by the manufacturer for 
photovoltaic applications or a voltage of: 
 
i) 1.80 V for lead acid cells, or  
ii) 1.00 V for nickel cadmium cells, 
 
if the manufacturer does not specify a final voltage. 
 
f) Determine the actual capacity from the following equation:  
C
a = I20 × t 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  17 where, 
Ca = actual capacity, in ampere hours 
 
I20    = discharge current, in amperes 
 
t    = discharge time in hours 
 
g) Recharge the battery in accordance with 7.1.3 
 
h) Perform steps (c) to (g) five times. 
 
8.1.3 Ca shall be equal to, or higher than, C20. If not, the procedure should be repeated. The rated 
value shall be reached at or before the fifth discharge. 
 
8.1.4 Reporting the results 
 
The following shall be reported:  
a) battery details 
 b) the capacity of the battery at each of the five discharges 
 
c) reference to this test method  
 
8.2 Cycle life 
 
8.2.1 The test shall be carried out on at least thr ee units (monoblocs or single cells). It shall have 
met the requirements of 8.1.3. 
 
8.2.2 Throughout the whole test period the battery sha ll be kept at an ambient temperature of 25 °C 
± 2 K. 
 
8.2.3 The battery shall be connected to a device wher e it undergoes a continuo us series of cycles, 
each cycle comprising: 
 
⎯ a discharge for 3 h at a current I = 3.4 × I20, or a discharge for 2 h at a current I = 5 × I20 
immediately followed by 
 
⎯ a recharge 
 
 for 9 h in case of discharge for 3 h at I = 3.4 × I20 or 
 
 for 6 h in case of discharge for 2 h at I = 5 × I20  
 
at constant voltage Uc or with constant current Ic (see 7.1.3) 
 
At the end of each 3 h or 2 h di scharge period the on-load voltage U’f shall be recorded automatically 
or be otherwise measured by suitable means. 
 8.2.4 After a series of (50 ± 5) cycles the battery shall be recharged according to 7.1.3. Then the 
capacity shall be determined by discharging with I = 3.4 × I
20 or 5 × I20 until Uf = n ×1.65 V. If the 
discharge time is greater than 3 h or 2 h respective ly, then the battery shall undergo another series of 
(50 ± 5) cycles according to 8.2.3. 
 
8.2.5 If in the course of this cycling the voltage U’f (see 8.2.3) falls below n × 1.65 V, then cycling 
shall be interrupted and the battery shall be re charged according to 7.1.3. The capacity Ca shall then 
be determined according to 8.2.4. If the discharge ti me is less than 3 h or 2 h respectively, then the 
test shall be terminated. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
18 © EAC 2008 — All rights reserved 8.2.6 The endurance is expressed as the total number of cycles according to 8.2.3 to which the 
battery can be submitted until the discharge time with I = 3.4 × I20 is less than 3 h or discharge time 
with I = 5 × I20 is less than 2 h. This translates to the termination of the endurance test when the 
capacity falls below 80 % of that determined in 8.1.3. 
 
8.3 Charge retention test 
 
A battery which has met the requirements of 8.1.3 s hall be charged according to 7.1.3. The surface 
shall be cleaned and dried. It shall then be stored on  an open circuit for 92 days (for vented lead acid 
types) or 120 days (for valve regulated lead acid types)  at an ambient temperature of 20 °C ± 2 K, or 
25 °C ± 2 K. 
 The battery shall then be discharged accordi ng to 8.1.2 with the discharge current I
20. 
 The duration t of the discharge to U
f = n × 1.75 V shall be equal to, or higher than, 15 h. The 
measured capacity shall be not less than 82 % of the actual capacity. 
 
8.4 Cycle endurance test in photovoltaic application (extreme conditions) 
 
In photovoltaic applications the battery will be ex posed to a large number of shallow cycles but at 
different states of charge. The cells or batteries shall therefore comply with the requirements of the 
test below, which is a simulation of the photovoltaic energy system operation.  
 
The cycle endurance test is an accelerated simula tion in extreme conditions of the battery operation 
in a photovoltaic energy system and shall be conduct ed by submitting the cells or monobloc batteries 
to a period of 150 cycles (50 cycles with t he phase A and 100 cycles with the phase B).  
 
Test samples shall be set up in accordance with the applicable standards listed in 7.1.5 after control 
of the capacity test in 8.1.  
 
Start the test with the battery fully charged. Bri ng the battery to a temperature of 40 °C ± 3 °C and 
stabilize for 16 h. Maintain the battery at 40 °C ± 3 °C throughout the test. 
 8.4.1 Phase A: shallow cycling at low state of charge 
 
 Lead-acid batteries 
 
 
a) Discharge the battery with a current I10 (A) during 9 h or until 1.75 V/cell is reached.  
 
b) Recharge 3 h with a current 1.03 × I10 (A)   
 
c) Discharge 3 h with a current  I10 (A).  
 
 Nickel-cadmium batteries  
 
a) Discharge the battery with a current It /10 (A) during 9 h or until 1.00 V/cell is reached.  
 
b) Recharge 3 h with a current 1.03 × It /10 (A)  
 
c) Discharge 3 h with a current  It /10 (A) 
 For both battery types, repeat b) and c) 49 times. Re charge the battery to the fully charged condition 
according to the manufacturer recommendations and continue the phase B. Phase A is summed up in 
Table 8. 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  19 Table 8 — Phase A: Shallow cycling at low state of charge 
 
 Discharging time 
h Charging time h  Lead-acid current 
A Nickel-cadmium current 
A 
a)  9  I10 (A) It /10 (A) 
   (or stopping at 1.75 V/cell) (or stopping at 1.00 V/cell) 
b)   3 1.03 I10 (A) 1.03 It /10 (A) 
c) 3  I10 (A) It /10 (A) 
Repeat b) to c) 49 times and continue to phase B  
 
8.4.2 Phase B: shallow cycling at high state of charge 
 
 Lead-acid batteries 
 
a) Discharge the battery for 2 h with a current 1.25 I10 (A) 
 
b) Recharge 6 h with a current I10 (A). The charge voltage shall be limited to 2.40 V/cell, unless 
otherwise specified by the manufacturer. 
 
 Nickel-cadmium batteries 
 
a) Discharge the battery for 2 h with a current 1.25 It/10 (A) 
 
b) Recharge for 6 h with a current It/10 (A). The charge voltage shall be limited to 1.55 V/cell unless 
otherwise specified by the manufacturer. 
 
For both batteries, repeat a) and b) 99 times and then perform a capacity determination according to 
8.4.3. Phase B is summed up in Table 9. 
 
Table 9 — Phase B: Shallow cycling at high state of charge 
 
 Discharging time  
h Charging time 
h Lead-acid current  
A  Nickel-cadmium current  
A 
a) 2  1.25 I10 (A) 1.25 It /10 (A) 
b)  6 I10 (A)  
(charge voltage limited to 2.40 
V/cell unless otherwise specified 
by the manufacturer) It /10 (A)  
(charge voltage limited to 1.55 
V/cell unless otherwise specified 
by the manufacturer ) 
Repeat a) to b) 99 times 
 
8.4.3 Capacity check 
 
After the phase B, the battery is cooled down to the temperature defined in the relevant standard as 
described in 7.1.5 and stabilized at this value for 16 h. The capacity test ( C20 for lead-acid batteries 
and C5 for nickel-cadmium batteries) is carried out acco rding to the relevant standard as described in 
7.1.5. 
 
8.4.4 End of test condition 
 
⎯ Capacity is checked after each per iod of 150 cycles (phases A + B). 
 
⎯ The value of actual capacity determined in 8.4.3 shall be recorded. 
 
⎯ The cycle life shall be expressed in num ber of 150 cycle (A+B) sequences completed. 
 
⎯ The test is finished:  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
20 © EAC 2008 — All rights reserved  During the phase A: when the cell voltage measured in discharge is lower than 1.5 V/cell for 
lead acid batteries and 0.8 V/cell for nickel-cadmium batteries.  
 
 After the phase B: when the checked capacity  measured in 8.4.3 is lower than 80 % of the 
rated capacity.  
 
8.4.5 Water consumption of flooded battery types and cells with partial gas recombination  
 
During the cycle endurance test, vented type cells or monoblocs may be topped up with water. The 
amount of water added shall be measured and reported.  
 8.4.6 Requirements 
 The number of complete cycle sequences (150 cycl es) achieved at the end of the test shall be not 
less than the value stated by the manufacturer. 
 
8.5 Charge acceptance after deep discharge 
 
8.5.1 The test shall be carried out on at least three units (monoblocs or single cells). The battery 
shall have met the requirements of 8.1.3. 
 
8.5.2 A load resistor is selected so that, from a voltage of n × 2 V, a current of I = 40 × I20± 10 % 
results. The resistor shall be connected to the te rminals of the battery, which shall then be stored for 
360 h at an ambient temperature of 20 °C ± 2 K or 25 °C ± 2 K. 
 8.5.3 The load resistor shall then be disconnected from the terminals and the battery shall be 
recharged at a constant voltage U
c (see 7.1.3) for a period of 48 h with an available current between  
6 × I20 and 10 × I20. 
 
8.5.4 At the end of the charging period,  the battery shall remain on open circuit at 25 °C ± 5 K for 
16 h to 24 h. It shall then be discharged according to 8.1.2. 
 
8.5.5 The resulting capacity in ampere-hours shall be ≥0.75 × C20 (Ah). 
 
8.6 Short-circuit current and internal resistance determination 
 
8.6.1 The test shall be carried out on a minimum of three cells which, after submission to the 
capacity test in accordance with 8.1, have been found to have a capacity Ca. 
 
8.6.2 After preparation in accordance with 7.2, the cells  or batteries shall be placed in a chamber at 
the appropriate ambient temperature until the temper ature of the electrolyte reaches (20 ± 2) °C. 
 
8.6.3 The discharge characteristic U = f(I) shall then be established by de termining two of its points 
in the following way.  
8.6.3.1 First point ( U
1, I1) 
 
After 20 s discharge at a current I1 = 4 I10 … 6 I10 (A) the voltage and current are read and give the 
first point. The discharge shall be interrupted after 25 s maximum; without recharging and, after an 
open-circuit stand of 2 min to 5 min,  the second point is determined. 
 
8.6.3.2 Second point ( U2, I2) 
 
After 5 s discharge at a current I2 = 20 I10 … 40 I10 (A) the voltage and current are read and give the 
second point. 
 
8.6.4 The characteristic U = f(l) is linearly extrapolated to U = 0 (V). The intercept indicates the 
short-circuit current Isc. The internal resistance ( Ri) may also be determined. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  21 
 
 
Figure 1 — Discharge characteristic U = f(I) 
 
From Figure 1, it follows that 
 
2 112 21
SCUUIUIUI−−=  A 
 
1 22 1
iIIUUR−−=  Ω 
 
NOTE 1 The voltage is measured at the terminals at the outlet of each cell or monobloc in order to ensure that no external 
voltage drop interferes with the test. A typical test circuit is shown in Figure 2. The values of short-circuit current and int ernal 
resistance obtained in this test refer to a single cell or monobl oc. However, the resistance of intercell connections has to be  
taken into account when calculating the short-circuit current and internal  resistance for a complete battery. 
 
NOTE 2 This test method provides information in stabilized test conditions and does not indica te dynamic reactions occurring, 
for example, during the first few milliseconds  of a short circuit. The results of this test have an accuracy which is of the or der of 
10 %. 
 
NOTE 3 In the case of very large cells the Ir and Scc value can be derived from smaller ce lls having the same plate size and 
type 
 
 
 
Figure 2 — Typical test circuit PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
22 © EAC 2008 — All rights reserved  
8.7 Mechanical endurance tests — Thermal cycling 
 
8.7.1 Procedure 
 
The procedure shall be as follows:  
a) Select a battery that has satisfied the capa city requirement of 8.1 and the charge retention 
requirement of 8.3. 
 
b) Prepare the battery for test in accordance with 7.2. 
 c) Determine the internal resistance of the battery in accordance with 8.6. 
 
d) Maintain the battery at an ambient temperature of 0 ± 2 °C for 12 h and then at an ambient 
temperature of 50 ±2 °C for 12 h 
 
e) Perform Step (d) six times.  
f) Maintain the battery at an ambient temperature of 10 ± 2 °C for 12 h and then at an ambient 
temperature of 40 ± 2 °C for 12h. 
 
g) Perform step f) 28 times. 
 h) Repeat steps b) and c). 
 
8.8 Mechanical endurance tests — Bump test 
 
8.8.1 Procedure 
 
The procedure shall be as follows: 
 
a) Select a battery that has satisfied the capa city requirement of 8.1 and the charge retention 
requirements of 8.3. 
 
b) Prepare the battery for test in accordance with 7.1. 
 
c) Determine the internal resistance of the battery in accordance with 8.6.  
d) In accordance with IEC 60068-2-29, subject t he battery to a series of 1000 bumps of 6 ms 
duration at 245 m/s
2. 
 
e) Repeat steps b) and c) 
 8.8.2 Any leakage of electrolyte or any change in internal resistance of greater than 25 %. 
 
8.9 Mechanical endurance tests — Drop test 
 
8.9.1 Procedure 
 
The procedure shall be as follows: 
 
a) Select a cell or monobloc that  has satisfied the requirements of  8.1.3 and the charge retention 
requirement of 8.3. 
 
b) Prepare the battery for test in accordance with 7.1.  
(c) Determine the internal resistance of the battery in accordance with 8.6. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  23 d) In accordance with IEC 60068-2-31, drop the cell or monobloc twice on its base on a solid floor 
from a height of 100 mm. 
 
e) Repeat steps b) and c).  
8.9.2  Any leakage of electrolyte or any change in  internal resistance of greater than 25 %. 
 
8.10 Mechanical endurance tests — Vibration test 
 
8.10 Procedure 
 The procedure shall be as follows: 
 
a) Select a cell or monbloc that has satisfied the requirements of 8.1.3 and the charge retention 
requirement of 8.3. 
 
b) Prepare the battery for test in accordance with 7.1. 
 
c) Determine the internal resistance of the battery in accordance with 8.6. 
 
d) In accordance with IEC 60068-2-6, mount the cell or monobloc in an upright position and vibrate 
it: 
 
i) at 6 mm constant displacement from 5 Hz to 13 Hz; and 
 
ii) at 19.6 m/s from 13 Hz to 150 Hz. 
 
This step shall be performed in three mu tually perpendicular planes in turn. 
 
e) Repeat steps b) and c)  
8.10.2 Any leakage of electrolyte or any change in internal resistance of greater than 25 %. 
 
8.11 High rate discharge capability 
 
8.11.1 A fully charged battery (7.1.3) shall be kept on open circuit for 16 h to 24 h. 
 
8.11.2 It shall then be discharged with the current Im = 40 × I20 for 300 s. 
 
8.11.3 The battery shall be recharged according to 7.1.3 and shall be left on open circuit at  
25 °C ± 2 K for 16 h to 24 h. 
 
8.11.4 It shall then be discharged with the current Ih = 200 × I20 for 5 s. 
 
8.11.5 Upon inspection, no apparent physical damage fr om these discharges shall be observable. 
 
8.11.6 The battery shall be recharged according to  7.1.3 and shall then be discharged with the 
current Im. The duration t of the discharge to Uf = n × 1.34 V shall be equal to, or higher than, 150 s. 
 
8.11.7 If the manufacturer has declared values of Im and Ih other than those in 6.9, the test currents 
of 8.11.2 and 8.11.4 shall be amended accordingly. 
 
8.12 Overcharge resistance test method 
 
8.12.1 Apparatus 
 
The apparatus listed in 7.2 are required.  8.12.2 Procedure 
 
The procedure shall be as follows: 
 
a) Select a battery that has sati sfied the capacity requirement of 8.1.3 and record the available 
capacity of the battery. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
24 © EAC 2008 — All rights reserved  
b) Prepare the battery for test in accordance with 7.1. 
 
c) Maintain a battery temperature of 40 ± 2 °C. 
 
d) Charge the battery for 250 hours at the 0.3C 20 rate. 
 
e) Allow the battery to c ool to a temperature of 25 ± 2°C. 
 
f) Recharge the battery in accordance with 7.1.3. 
 
g) Determine the actual capacity of t he battery in accordance with 8.1.3. 
 
8.12.3 Calculation 
 
The loss of capacity, expressed as a percentage,  shall be determined from the following equation: 
 
asae as
L,40100) (
CCCC× −=  
 
where, 
 
CL,40 = loss of capacity, at 40 °C, per 250 h, expressed as a percentage 
 
Cas = actual capacity at the st art of the test, in ampere hours 
 
Cae = actual capacity of the battery at  the end of the test, in ampere-hours. 
 
NOTE The percentage loss of capacity per month at 25 °C is half that at 35 °C. 
 
8.12.4 Reporting the results 
 
The following shall be reported: 
 
a) Battery details. 
 
b) The percentage loss of capacity determined in 8.12.3. 
 
c) Reference to this test method.  
8.13 Content and durability of required markings 
 8.13.1 The test shall be carried out on three of the required markings in their definitive size, form, 
material and execution. Required markings may be printed, painted or moulded on the case or cover 
or included in a label affixed to the case or cover. 
 
8.13.2 The test shall consist of visual verification of a) the presence and b) the legibility of all the 
required markings before and after exposure to selected chemicals.  
 
8.13.3 The durability of the marking shall be tested as follows:  
 
8.13.3.1 Test with water and aliphatic solvent 
 
The procedure is as follows:  
 
a) A label or marking shall be rubbed for 15 s with a piece of cloth soaked with water and again for 
15 s with a piece of cloth soaked with petroleum spirit, dried in air and then inspected visually.  
 
b) The petroleum spirit used for this test shall be n-hexane (C 6H14 – alkane C 6) with an initial boiling 
point of 65 °C, a dry point of approximately 69 °C , a density of 0.7 kg/l and a maximum aromatic 
hydrocarbon content of 0.1 % per volume.  
 
8.13.3.2 Test with neutralizing solutions  
 
The procedure is as follows:  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  25 A new label or marking shall be rubbed for 15 s with a piece of cloth soaked with a saturated solution 
of sodium carbonate (Na 2CO 3) or bicarbonate (NaHCO 3) in water, dried in air and then inspected 
visually. 
 
8.13.3.3 Test with electrolyte  
 
The procedure is as follows:  
 
A new label or marking shall be rubbed for 15 s with a piece of cloth soaked with a solution of 40 % in 
weight of H 2SO 4 in water, washed with water, dried in air and then inspected visually. 
 
8.13.4 Each required label or marking shall be visually inspected, fully described and depicted 
photographically before and after the ap plication of the test chemical.  
 
IMPORTANT: Solvents shall not be used to clean cells and monobl oc batteries as otherwise damage to the plastic components 
may result. Approved cleaning fluids are only thos e expressly specified by the manufacturer.  
 
NOTE The content of the required markings is specified in 5.3. 
 
9 Guarantee 
 
Guarantees against faulty workmanship and material for a period specified by the manufacturer but of 
at least one year shall be given.  
 
10 Marking 
 
10.1 Marking on battery 
 
The following information shall be permanently marked on the cell or battery:  
a) The name of the manufacturer or supplier or  his/her trademark and type reference number; 
 
b) Country of origin; 
 
c) Type of battery; 
 
d) Date of manufacture (month and year); 
 e) Rated capacity at C
20 discharge rate at 25 °C; 
 
f) Nominal voltage; and  
g) Cleary marked and sized terminal polarity signs. 
 
h) Electrolyte density (fully charged at 25 °C); 
 
10.2 Information to be supplied on the package 
 
Information relevant to safety recommendations as  required by local, national or international 
regulations shall be marked on the cell or monobloc package. 
 
The manufacturer or supplier shall supply the following information: 
 a) recommended depth of discharge; 
 
b) cycle life; 
 
c) maximum charge voltage, float voltage and load disconnect voltage; 
 
d) temperature compensation curves; 
 
e) type of battery cell and 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
26 © EAC 2008 — All rights reserved f) voltage (battery); 
 
g) manufacturer's or supplier's type reference; 
 
h) ampere-hour capacity with rate of discharge and end voltage at the chosen reference 
temperature; 
 
i) electrolyte density (fully charged at the chosen reference temperature); 
 
j) statements on safety recommend ations, operation and maintenance. 
 
10.3 Marking of polarity 
 
10.3.1 General provision for marking of cell polarity 
 
To comply with this standard, stationary battery cells and monoblocs shall carry the polarity marking, 
at least of the positive terminal. 
 
10.3.2 Form of marking 
 
The marking shall take the form of the symbol + , indented or in relief, on the lid adjacent to the 
positive terminal. 
 
The marking of the negative terminal shall take the form of the symbol − , indented or in relief, on 
the lid adjacent to the negative terminal. 
 10.3.3 Symbols used for marking and their dimensions 
 
Symbols used for marking of the polarity shall be in accordance with IEC 60417. 
 
The marking of the positive terminal shall be in accordance with the symbol 60417-IEC-5005, Positive polarity. 
 
The marking of the negative terminal shall be in  accordance with the symbol 60417-IEC-5006, 
Negative polarity. 
 
The actual value of the dimension “a” of these symbols shall be greater than, or equal to, 5 mm. 
 
NOTE A dimension “a” of 5 mm corresponds to a total length of each arm of the symbol equal to 6 mm. 
 
11 Recommended use of tests 
 
11.1 Type test 
 
Type tests are: 
 
⎯ the rated capacity test and the charge retention test; 
 
⎯ the endurance test in cycling; 
 
⎯ the cycling endurance test in photovolta ic application (extreme conditions).   
 
The minimum number of cells or monobloc batteries shall be as specified in the relevant standards 
listed in 7.1.5. 
 
The cycling endurance test in photovoltaic applicat ion shall be performed with a minimum of six cells 
or 2 monobloc batteries.  PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  27 11.2 Acceptance test 
 
11.2.1 Factory test  
 
The acceptance test shall be agreed between the cust omer and the supplier. Compliance to marking, 
labelling or to the rated capacity may be verified. 
 
11.2.2 Commissioning test  
 
A commissioning test is recommended to prove the int egrity of the installed bat tery system by means 
of a capacity test. 
 
12 Safety 
 
Refer to the manufacturer's instructions for procedures to be observed during installation, commissioning, operation, taking out of service, and disposal. 
 
13 Documentation 
 
Refer to the manufacturer's documentation for tr ansport and storage, commissioning, putting into 
service, operation and maintenance. 
 
The manufacturer shall advise if there are special c onsiderations for the initial charging of batteries 
with only the solar array available as the power source. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
28 © EAC 2008 — All rights reserved  
Annex A 
(informative) 
 
Ten-hour rate capacity (10 hour discharge rate) 
 
A.1 Apparatus 
 The apparatus listed in 7.2 is required. 
 
A.2 Procedure 
 
The procedure shall be as follows: 
 
a) Prepare the battery for test in accordance with 7.1. 
 b) Monitor the temperature of one of the cells of each  battery under test, or of each cell or monobloc 
if a single cell or monobloc is being tested. The cell chosen to monitor the temperature of the battery should not be a cell at either end of the battery. 
 
c) Discharge the battery at the 0.1C
10 rate. The discharge shall commence between 1 h and 24 h 
after the battery has reached fu ll charge, and shall be performed at  a battery temperature of 25 ± 
2 °C. The discharge current shall be held within ±1 % of the required rate. 
 
d) During the discharge, record t he following at hourly intervals: 
 
i) battery voltage; 
 
ii) discharge current; and  
 
iii) battery temperature. 
 e) End the discharge when the battery reaches t he final voltage specified by the manufacturer for 
stand-alone applications or a voltage of: 
 
i) 1.85 V for lead acid cells, or 
 
ii) 1.00 V for nickel cadmium cells, 
 
if the manufacturer does not specify a final voltage. 
 
f) Determine the actual capacity from the following equation: 
 
Ca = I × t 
where, 
Ca = actual capacity, in ampere hours 
 
I    = discharge current, in amperes 
 
t    = discharge time in hours 
 
g) Recharge the battery in accordance with 7.1.3 
 
h) Perform steps b) to g) ten times. 
 A.3 Reporting the results 
 
The following shall be reported: 
 
a) battery details 
 
b) the capacity of the battery  at each of the ten discharges 
 
c) Reference to this test method PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  29  
Annex B 
(informative) 
 
Lead acid battery technologies 
 
B.1 Battery applications 
 
Lead acid batteries are almost universally used in PV systems because of their low cost and 
availability. A few special ap plication PV systems use nickel- cadmium batteries or advanced 
technologies to improve reliability and/or to reduce  maintenance. This is a very small percentage of 
the applications, and as a result, this document will only address the lead-acid battery technology. At 
present, the dominant lead-acid battery technologies used in PV systems are divided into two major 
groups, vented (flooded) lead-acid batteries and valv e-regulated lead-acid batteries that have their 
electrolyte contained in a medium of either glass fibres or gel. Batteries from both subgroups are 
designed for starting, lighting, and ignition (SLI),  deep-cycle marine/recreational vehicle (RV), deep-
cycle golf cart, deep-cycle industrial motive power, small float service stationa ry uninterruptible power 
supply (UPS), and large stationary float service applic ations. Each of the above battery applications 
will also have a number of options  available for the six major ba ttery markets indicated above. 
Generally standalone PV systems use batteries de signed for the SLI automotive, deep-cycle marine/ 
RV, or deep-cycle motive power gol f cart markets. The most relevant to PV systems are the vented 
and VRLA deep-cycle batteries. Even though automot ive SLI batteries are not designed for deep 
cycling and have a significantly sh orter cycle-life, they are univers ally available and are the lowest 
initial cost short-term option. The common deep-cy cle marine/RV batteries are designed to be more 
tolerant to deep cycling. Motive power golf cart batteries are designed for deep cycle service with 
cycle-life ratings significantly gr eater than the deep-cycle marine/RV batteries. Motive power and/or 
golf cart batteries are not readily available in auto parts stores.   
B.2 Vented lead acid batteries 
 When used and maintained properly, the vented lead acid battery has a long and successful track 
record for providing power in SLI, deep-cycle mo tive power, and standby stationary float service 
applications. Each of these major categories uses ba tteries specifically designed for that application. 
The key for successful battery operation is to use the appropriate battery for the application, provide 
the required maintenance, and provide a cycle pr ofile consistent with the battery design. 
 
If SLI batteries are used in PV systems, it is import ant to understand their use, design, and limitations. 
Most vented SLI batteries now used in developed co untries are of the lead-calcium open vent design. 
SLI batteries are designed to be used for short high-rate discharges in engine starting and to provide brief lighting loads. The battery grids are specially  designed for this application by making them thin 
for more surface area and alloying them with lead-calcium to reduce water consumption and maintenance. The thin grids are susceptible to cracking and grid corrosion from the mechanical 
stresses of cycling and the normal el ectrochemical wear out processes. 
 Another group of SLI batteries used in PV systems in developing countries have a similar design to 
the above SLI batteries except that they use a low percentage of antimony (~2%  to 3%) in the lead 
grids and they have slightly thicker grids. These batteries are similar to SLI batteries used in developed countries up until the 1960s, but they ar e still common in developing countries and are 
similar to deep-cycle marine/RV batteries presently in use in developed countries. In these batteries, 
the grids are slightly thicker and the 
 
Antimony grid alloy is more resistant to cracking, stratification, and premature capacity loss. Cycle-life 
is greater than the lead-calcium batteries but is much less than the motive power and golf cart 
batteries. In many countries, this may be the only battery available, and with proper care, they can 
have an average life of 1.5 years. 
 The marine/RV batteries are a deep-cycling battery that is very popular with the PV industry. The 
construction is similar to the lead-antimony SLI ba tteries except that the grids are thicker, more 
antimony is used as an alloying element in the grids, the positive paste active material is formulated PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
30 © EAC 2008 — All rights reserved for cycling applications, and more space is provi ded for plate sediment. The combination of these 
design improvements results in a significant impr ovement in cycling ability without a significant 
increase in cost. 
 The deep-cycle golf cart batteries are medium-duty cy cling batteries that are also very popular with 
the PV industry. The construction of these batteries includes grids with a medium thickness of 3 to 4 mm, a grid alloy with a relatively high antimony conten t in the 4 % to 6 % range, a positive plate active 
material designed for deep-cycling, and more space for plate sediment. The grid thickness provides 
extra strength and excess metal to delay the normal wear out mechanisms of grid corrosion and 
active material shedding. The additional antimony provides more resistance to grid corrosion and minimizes capacity loss over the life of the battery. A more robust positive active material is more 
tolerant to cycling stresses and maintains capaci ty over the life of the battery. Typically, the deep-
cycle battery designs require more watering and maintenance. The cost of deep-cycle golf cart 
batteries is somewhat more than marine/RV batteri es, but the cycle-life can be much greater. Due to 
volume production, the deep-cycle gol f cart batteries may provide the lowest life cycle cost option in 
properly designed small stand-alone PV systems. 
 
Industrial motive power forklift batteries represent  the most robust battery designs for deep-cycle 
battery applications. The major differences betwe en golf cart batteries and motive power forklift 
batteries are the plate thickness and the rating proc ess. Industrial motive power truck battery plate 
thickness is usually in the 5 to 6 mm range, and the capa city rating is usually at the 6 h rate. Golf cart 
batteries, on the other hand, are rated in minutes at a 75 ampere discharge rate or at the 20 h rate. 
This rating difference results in industrial motive pow er forklift batteries that are more conservatively 
sized. The cycle-life of these batteries is generally more than twice that of golf cart batteries, but their 
cost is also higher.  
Industrial stationary batteries are also available for PV systems. These batteries can be used in deep-
cycling and shallow-cycling applications with good re sults, but they can be more costly than motive 
power batteries. Some cycling stationary batteries are designed to have a much lower water consumption rate compared with deep-cycle motive power batteries. This can be an important consideration in PV system design. 
 
B.3 VRLA batteries 
 VRLA batteries first became available in the early 1980s and have enjoyed a steady growth in 
production since then. VRLA batteries now repres ent a significant portion of the PV battery market. 
The VRLA technology is one of the most importa nt lead-acid battery devel opments in the twentieth 
century. The early marketing strategies promoted this battery as a "sealed" or "maintenance free" 
battery, which it is not. The VRLA battery uses the oxygen recombination cycle to return most of the 
gas produced from electrolysis back into water. Sm all quantities of water may be lost from venting of 
excess gas and from internal grid corrosion. VRLA batteries cost more, degrade faster at high temperatures, require more stringent charge contro l, and may have a lower cycle-life than the vented 
alternative. The impetus for using VRLA batteries is due primarily to the fact that no watering is 
required, minimal electrolyte residue is left on the ba ttery terminals, no special provisions for venting 
hydrogen gas other than room ventilation is usually required, installation requires less floor space, 
and the electrolyte is held immobilized in a glass mat or gel, which makes transportation safer and easier.  
VRLA batteries have three design features that ar e unique with respect to their vented counterparts. 
These unique features are the captive electr olyte, a cell pressure valve, and the oxygen 
recombination cycle. The Captive electrolyte is su spended in either glass fibres called the absorbed 
glass mat (AGM) or in the silica gel. In AGM and gel batteries, the hydrogen ions produced at the 
negative plate and oxygen gas produced at the positi ve plate recombine electrochemically at the 
negative plates to conserve water. The VRLA battery  technology does occasionally vent a very small 
amount of hydrogen and oxygen gas when it is unde r charge; consequently, the VRLA battery should 
be installed in a ventilated enclosur e. The venting occurs when a low-pr essure gas relief valve allows 
excess gas to vent when the battery reaches its maxi mum internal pressure. The valve also prevents 
air from entering back into the battery and ca using negative plate discharge from atmospheric 
oxygen. The valve is a critical part of the oxygen recombination cycle because it prevents PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  31 atmospheric oxygen from entering the battery. T he oxygen recombination cycle in Equation (B.1) 
includes the following chemical reactions: 
 
Positive plate releases O 2 on charge 
 
H2O ⇔ 2H + ½O 2 + 2e  (B.1) 
 
O2 passes through AGM or gel to the negative plate 
 
Pb + ½O 2 ⇔ PbO 
 
PbO + H 2SO 4 ⇔ PbSO 4 + H 2O 
 
PbSO 4 + 2H++ 2e ⇔ Pb + H 2SO 4 
 
The required maintenance on VRLA batteries in stand -alone PV systems as compared with stationary 
float service applications is less  than on deep-cycle vented lead-a cid batteries. VRLA stand-alone PV 
system maintenance usually involves retorquing electrical interconnections, removing corrosion, 
measuring cell or monoblock voltages, and ensuring t hat the battery charger is working properly and 
meeting manufacturer's charge requirements. 
 
B.4 Battery selection 
 
Battery selection is dependent on battery availabilit y, application, performance, cost, and system size. 
Because lead-acid batteries are heavy and contain sulfuric acid, shipping them can be difficult and result in damaged batteries. In many remote or developing country locations, it may be more practical 
to use local batteries, because replacement batteries may be needed in the future. When vented deep-cycle lead antimony batteries are available, th ey may be the lowest life cycle cost option. In 
applications where battery watering is not possible, or very expensive, or w here shipping of liquid 
electrolyte is difficult, the VRLA battery can be a cost-effective option. With larger PV systems, the 
batteries will also need to be larger. Generally, the maximum number of parallel strings is four. Above 
this size, larger batteries should be used. The la rger batteries are typically the deep cycle industrial 
forklift batteries or large stationary batteries. Th ese batteries can be used in battery banks with 
capacities well over 10 000 Ah.  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
32 © EAC 2008 — All rights reserved  
Annex C 
(informative) 
 
Lead-acid battery characteristics 
 
C.1 Self-discharge 
 All lead-acid batteries are subject to self-discharge or  "local action" at all times. The effect of self-
discharge only becomes a problem when batteries ar e left in storage without freshening charges. The 
self-discharge rate is a function of temperature, grid alloy, battery age, acid-specific gravity, and 
battery design. Self-discharge is a result of ongoing  internal electrochemical reactions that essentially 
act as a continuous battery load. The most effectiv e method to minimize self-discharge is to lower 
battery temperature. Lead-calcium grid alloys also greatly reduce self-discharge. Damage to batteries 
in storage due to self-discharge is only prevented by providing freshening charges on a regular basis. 
 The self-discharge rate for new-vented deep-cycle high- antimony batteries is about 2.5 % per week at 
25 °C. The self discharge rate increases dramatically at 40 °C to over 5 % per week and decreases to 
less than 1 % per week at 0 °C. The self-discharge rate also increases significantly as the battery 
ages. Generally battery manufacturers will recomm end a freshening charge every month or two for 
most vented deep-cycle batteries.  
The self-discharge rate for a deep- cycle vented low-antimony grid allo y battery is about 1 % per week, 
whereas the lead-calcium alloys grids and VRLA bat teries are typically less than 1 % per week at  
25 °C. For VRLA batteries at 40 °C, the self-discharge rate is about 2.5 % per week, and at 0 °C, the self-discharge is near zero. The vented lead-calci um battery usually has only a slightly higher self-
discharge rate compared with the VRLA battery . Battery manufacturers recommend a freshening 
charge about every six to seven months fo r vented lead-calcium and VRLA batteries. 
 
C.2 Temperature effects 
 Battery temperature has a significant impact on cy cle-life, capacity, charge voltage, electrolyte-
specific gravity, and water consumption. Most lead-acid batteries are rated for operation at 25 °C; 
therefore, most battery sp ecifications will be for operation at 25 °C. If the battery is used at other 
temperatures, then the specifications  for cycle-life, capacity, charge  voltage, electrolyte specific 
gravity, and water consumption will need to be adjusted accordingly. 
 The useful life of vented stationary float-service ba tteries will decrease by abo ut 50% if the battery 
temperature increases 10 °C (35 °C battery temper ature). If the battery operating temperature drops 
10 °C to 15 °C, then the life will increase by about 10%. Although the exact temperature/life 
relationship for deep cycle batteries is not known, a similar relationship should hold because the 
degradation mechanism is the same as for float-service batteries. 
 Cycle-life of VRLA batteries is much more dependent  on temperature, but the exact value of reduction 
in cycle-life is not known. However,  it is known that the VRLA cycle- life reduction is greater than that 
of deep-cycle batteries for every 10 °C increa se in battery temperature over 25 °C. 
 
The capacity of all lead-acid batteries is affe cted by temperature. The capacity temperature 
relationship is not linear, but for most operatin g temperatures, a 1 %/°C temperature/capacity 
relationship is acceptable. As the rated capacity is  at 25 °C, the capacity increases above 25 °C and 
decreases below 25 °C by the specified Amount.  
 
Battery charge or regulation voltage needs to be adj usted by about -0.005 V/°C/cell as the battery 
temperature changes. The battery temperature compens ation value for a specific battery is normally 
provided by the battery manufacturer. Above 25 °C , the regulation voltage needs to be reduced, and 
below 25 °C, the regulation voltage needs to be incr eased. Equation (C.1) is the formula for cell 
temperature compensated regulation voltage: 
 
V
r /cell (Temp Comp) = ((Bat Temp — 25 °C) x -0.005) + Vr /cell @ 25 °C  (C.1)  PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  33  
The need for temperature-compensated regulation  voltage in PV systems occurs when battery 
temperatures deviate from 25 °C. Without temperat ure compensation, the lead-acid battery will not be 
fully charged at low temperatures and will be excessively charged at high temperatures. 
 C.3 Electrolyte management  
Vented deep-cycle lead-acid batteries require addition  of pure water to the electrolyte. Usually, water 
additions are required every one to six months depe nding on battery design and how old the battery 
is. Older batteries require more water. Only very ra rely will vented batteries require more electrolytes. 
Electrolyte additions would only be needed if a cell l eaks electrolyte. VRLA batteries generally cannot 
be watered and thus do not require any water additions. 
 
Water consumption increases at higher battery temp eratures and decreases at lower temperatures, 
and thus, maintenance should be increased or decreas ed accordingly. Most of the increased water 
loss is due to the lower electrolysis voltage at higher temperatures and the venting gas that carries with it the products of electrolysis and water vapour. 
 Electrolyte specific gravity is also affected by  temperature and needs to be adjusted accordingly 
depending on both specific gravity and temperature.  Because a temperature-compensated specific 
gravity measurement requires a spec ific gravity and temperature meas urement, the coefficient for that 
specific gravity is usually obtained from a table. For example, at a measured specific gravity of 1.300 
at 0 °C, the specific gravity needs to be adjus ted downward by 0.000738/°C  to 1.282 to obtain a 
reading at 25 °C. At 40 °C, the same temperature- compensated specific gravity would read 1.271. 
Specific gravity tables can be obtained from t he manufacturer's installation and operation manual. 
 Electrolyte stratification is caused when the heavie r acid formed by the decomposition of sulfates on 
recharge migrates to the bottom of the battery and the lighter water/electrolyte mixture moves to the 
top of the battery. The non-uniformity in acid dist ribution causes unequal electrode utilization, reduced 
capacity, and premature electrode failure. If the gassi ng on recharge in vented batteries is limited by a 
low-regulation voltage or is cut short, then the r equired mixing of the electrolyte will not occur. 
Recovery requires extended heavy gassing of the batte ry for hours at voltages at or above 2.40 V per 
cell. Undersized PV arrays and/or low-regulation voltages  are the major causes of battery stratification 
in PV systems. 
 
In addition to the temperature effects, there are a number of other factors t hat need to be considered 
when measuring electrolyte-specific gravity. These factors include the state of  charge of the battery, 
electrolyte water level, electrolyte stratification, an d the cycle history of the battery. The most useful 
specific gravity data for a PV system are obtained just after a normal charge cycle when there has 
been a high solar resource period where the battery has recovered from any previous discharges. 
This measurement will provide an operational specific gravity, which should be near the 
manufacturers specified value for that battery. In  cases where the electrolyte level is low, the 
measured value will be significantly higher than the specific gravity m easured at a full electrolyte level. 
Manufacturers specify specific gravity at a full el ectrolyte level. All spec ific gravity measurements 
should be at the same water level to reduce measur ement error. If specific gravity measurements are 
obtained at other than a high state of  charge, then significant error can also be introduced as a result 
of stratification and sulfation.  C.4 Cycle-life  
Lead-acid batteries designed for cycling applications usually have a manufacturer's rated cycle-life. The published cycle-life values are usually given at several different depths of discharge. The 
shallower the depth of discharge, the greater the cycle-life. It is impor tant to understand that the rated 
cycle-life is usually measured under optimum conditions. If battery use is under less than optimum 
conditions, then the expected cycle-life may be le ss due to other battery degradation mechanisms. 
Cycle-life ratings for vented dee p-cycle lead-antimony batteries ra nge from less than 200 deep-cycles 
for light-duty batteries to over 1500 deep cycles  at 80% DOD for heavy-duty industrial motive power 
batteries. The wear out mechanism is generally positive plate grid corrosion. The biggest difference 
between batteries with low and high cycle-life ratings is  the positive plate grid thickness. Battery cost 
is usually proportional to grid th ickness, cycle-life, and capacity. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
34 © EAC 2008 — All rights reserved  
The cycle-life of properly maintained and installed VRLA batteries is generally less than 300 deep-
cycles for light-duty batteries and less than 1200 deep-cycles at 80% DOD for heavy duty industrial 
VRLA batteries. VRLA battery cycle-life is usually limited by water loss and grid corrosion, but other 
degradation mechanisms may also limit cycle-life.  
C.5 Battery coulombic or ah recharge efficiency 
 
Battery coulombic efficiency is usually measured using the discharged Ah divided by the charged Ah. 
Lead acid battery charge efficiency is affected by  battery state of charge (SOC), battery design, 
battery grid alloy, charge rate, battery history, ba ttery age, and cycle DOD. The charge efficiency for a 
discharged vented battery is initially about 99%, and as the battery approaches higher states-of 
charge, the efficiency will drop off and approach zero near 100 % SOC. There are significant 
efficiency differences between v ented lead antimony and VRLA batteries. This is due to VRLA battery 
design and grid alloy. As a rough comparison, vented lead-antimony batte ries will be about 80% 
efficient and VRLA batteries will be about 90 % to 95 % efficient for 100 % DOD cycles. This means that to recharge VRLA batteries requires about 105 % to 110 % more Ah and to recharge vented 
lead-antimony batteries requires about 120 % more Ah. Most of the efficiency improvement in VRLA 
batteries is due to the grid alloy and the immobiliz ed electrolyte in conjuncti on with the valve-regulated 
vent caps, which facilitate the oxygen recombi nation process and eliminates the need to mix 
electrolyte.  
Efficiency is lower for vented batteries because of the electrolyte stratification and the required 
electrolysis on charge. In addition to stratifica tion and electrolysis, the battery history can make 
recharge considerably less efficient. If the battery is left in a discharged condition, then other battery 
degradation mechanisms such as "hard" sulfation a nd degradation of the positive active mass will 
result in a slower capacity recovery. To reco ver the lost capacity requires considerably more 
overcharge than the normal recharge and therefore lo wers charge efficiency. The exact efficiency 
value for a specific SOC will vary considerably depending on the above factors. Therefore, PV array 
sizing needs to be increased to accommodate these efficiency losses so that the battery can recover 
from extended periods in a discharged condition. 
 
C.6 Charge acceptance 
 Charge acceptance is a term used to describe the ra te at which the battery can be recharged. Charge 
acceptance is also related to the "ampere-hour law", where the charging rate in amperes is kept 
below a value equal to the number of ampere-hours to be charged into the battery. Using the "ampere 
hour law" for recharge, the battery should not gas excessively or overheat. Charging vented batteries 
in excess of the charge acceptance limit will tend to  result in secondary reactions such as electrolysis 
and will not reduce the time required to return the battery to 100 % SOC.  In PV systems, the charge rate is low, but the limited char ge acceptance is st ill a factor when the 
battery reaches about 80 % to 90 % SOC. At this poi nt, the charge current will  usually be limited by 
the regulation voltage. Any excess current will only be used in electrolysis to gas the battery, which is 
needed for destratification of vented batteries. T he charging current will continue to drop until the 
battery reaches 100 % SOC, and then only the electr olysis or gassing current will be left. The time 
required to achieve 100 % SOC would be an indication of charge acceptance and may be many hours. Another measure of charge ac ceptance is the number of Ah retu rned back to the battery within 
a fixed time period under a fixed voltage at a const ant temperature. It is important to understand that 
in PV systems, it is necessary to  ensure that there is an adequate PV a rray size to provide the battery 
with sufficient charge to recover from the previous discharge cycle. 
 
C.7 Sulfation 
 Sulfation is the normal result of battery discharg e when lead-sulfate forms on the surface and in the 
pores of the active plate material [see Equation (C.2)]. 
 
Positive Plate 
 
PbO 2 + 4H++ 2e ⇔ Pb2+ + 2H 2O  (C.2) 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  35 Pb2+ + SO−2
4⇔ PbSO 4 
 
Negative Plate 
 
Pb ⇔  Pb2++ 2e 
 
Pb2+ + S0−2
4⇔ PbSO 4 
 
Sulfation becomes a problem when large crystals of  lead sulfate form on the active material as a 
result of inadequate charging and battery neglect or mi suse. It is difficult, by charging, to decompose 
these large lead sulfate crystals in order to return their sulfate ions back to the electrolyte. This 
effectively reduces battery capacity and life. Large  sulfate crystals may be detectable by a hard rough 
surface on the active plate material or a low specif ic gravity after an equalization charge. This is called 
excessive sulfation or "hard" sulf ation. "Hard" sulfation is caused by some of the following form of 
abuse: 
 — Allowing the battery to stand in a discharged condition for an extended period of time 
 
— Adding additional electrolyte to the battery cells instead of water.  
— Operating the battery while consistently undercharging it 
 Temperature fluctuations while the battery is standing  idle also play an important part in the growth of 
large sulfate crystals. When the temperature increase s, the smaller sulfate crystals dissolve in the 
electrolyte, and when the temperatur e decreases, the sulfate solubility is lower and the crystals slowly 
grow larger again. The temperature swings promote the slow growth of large sulfate crystals that 
would otherwise be small and more easily dissolv ed into the electrolyte. An undersized PV array 
and/or low-regulation voltage will result in consist ently undercharged batteries and "hard" sulfation in 
addition to other battery degradation processes.  
C.8 Hydration 
 
Hydration occurs when a lead-acid battery is over  discharged and left in the discharged condition for 
an extended period of time. Hydration is formed when lead is dissolved into solution with the water in 
the electrolyte that results from  over discharge. A hydrated battery  will have a white film around and 
between the plates. This lead-hydr ate film will inhibit charge, making the battery unrecoverable. 
 
C.9 Mossing  
Mossing can occur in vented cells where sloughed active positive material will circulate in the electrolyte and reform as negative material as it t ouches and adheres to the negative plate. A shorted 
cell may result when mossing occurs at the top of th e cell and bridges its separators. This process is 
also referred to as treeing.  
C.10 Battery mounting orientation 
 All vented batteries are required to be in the upright position, but VR LA batteries will operate in any 
position except upside down. The ma nufacturers of large industrial AGM VRLA batteries with plates 
over 0.4 m tall recommend that the battery be inst alled on its side. This reduces the height that 
electrolyte is required to wick up in the AGM and improves performance. Gel VRLA technology is 
unaffected by the mounting orientation.  
C.11 Life-cycle considerations 
 
To achieve the best cycle-life for a given applicat ion and battery requires the user to understand the 
battery design limitations, charge requirements, and maintenance requirements. Premature battery 
failures can generally be avoided by proper charge and/or installation and maintenance. 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
36 © EAC 2008 — All rights reserved C.12 Battery thermal runaway 
 
Under abnormal circumstances, battery thermal runa way can occur as a result of excessive charging 
at elevated temperatures. As the battery temperature increases, the electrolysis voltage drops, and 
this can result in excessive charge currents, which al so increase the rate at which the internal battery 
heating occurs. As temperature control is an import ant consideration, any ex ternal heating such as 
that from direct sunlight should be avoided. Without proper charge c ontrol, which includes 
temperature-compensated regulation voltage, this  process continues uncontrolled until the heat 
generated causes the plastic battery case to melt and vent, resulting in battery failure. Vented 
(flooded) batteries can dissipate heat much more e ffectively due to their exce ss liquid electrolyte, so 
the thermal runaway problem is predominately asso ciated with VRLA batteries because of their 
limited ability to dissipate heat. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  37  
Annex D 
(informative) 
 
PV system operational parameters 
 
D.1 Battery charging  
To prevent batteries in standalone PV systems fr om being undercharged, the charge regulation 
voltage must be set at the appropriate level, the PV ar ray to load ratio must be sufficient, and/or the 
solar resource must be sufficient for the system de sign. Charging batteries is not simple and can be 
accomplished with many different c harge profiles. As a rule of thumb,  charging at a higher regulation 
voltage requires less time at regulation voltage and charging at a lower regulation voltage requires 
more time at regulation voltage. The time spent on charge below the regulation voltage is called the 
bulk-charge phase, and the time at regulation voltage is usually called the finish-charge or taper-
charge or absorption phase of battery charging. PV systems operating during full sun periods may 
provide 2.5 h or less at regulation voltage every day , so most of the finish charge and, consequently, 
electrolyte mixing has to be done in that time period.  The variations in the seasonal solar resource 
where the sun may be obscured during winter months or rainy seasons also need to be anticipated. In 
these low resource periods, the battery may not  reach regulation voltage for weeks. This can 
seriously degrade the battery capaci ty even after an equalization charge. 
 The goal of battery charging is to return the battery  to a high SOC each cycle to minimize the capacity 
degradation resulting from deficit-c harge cycling. In addition to standard battery recharge, some 
battery applications will require an equalization or comp lete finish-charge at regular intervals to return 
the battery to 100 % SOC. Battery recharge is dep endent on battery technology and the cycle profile. 
These two factors will determine ho w the battery should be charged.  The battery charging parameters 
include regulation voltage, charge rate, time at r egulation voltage, battery temperature, temperature-
compensated regulation voltage, and equalization or  finish-charge voltages and times. The charge 
algorithm is a critical element in the performance of the battery; therefore, every effort should be 
made to use an acceptable charge algorithm fo r the battery and application. The important 
consideration for PV systems is whether the system is capable of recovering lost battery capacity 
from low solar resource periods during average so lar resource periods. If the time that the battery 
spends recovering from a discharge is excessiv e, then permanent capacity loss will result. The 
maximum safe recovery time is very dependent on the battery design. 
 
D.2 Battery equalization 
 An equalizing charge is intended to correct any c apacity, cell voltage, and/or specific gravity 
inequalities that may occur during service. It is a prolonged charge usually at an elevated voltage. The 
frequency of equalizing charge is dependent on the batte ry, charge algorithm, and cycle profile. Many 
manufacturers recommend an equalization charge every one to two weeks for daily use deep-cycle 
motive power industrial batteries. VRLA batteries may also require equalization charges and may or may not require an increase charge voltage. Equalizing VRLA batteries is recommended by the 
battery manufacturer when cell voltages become unba lanced or when the battery is left discharged for 
an extended time. A typical equalization charge fo r a VRLA battery may require 24 hours at the 
standard or slightly elevated regul ation voltage (2.35 or 2.40 V per cell). Therefore, VRLA battery 
equalization in PV systems may not be practical.  
Some PV charge controllers have a preset equaliz ation-charge function that is triggered based on 
lapsed time or battery voltage. Others have a ma nually triggered equalization-charge function. When 
these functions are engaged, they generally boos t the battery charging voltage for one day. The 
charge controller needs to reach the equalization vo ltage to complete the equalization charge. In most 
cases, the PV charge Controller equalization voltage is  not as high, the time at equalization voltage is 
not as long, and the frequency of equalization charging is not as often as is recommended by the 
battery manufacturer. This is because of the limit ed charge current available with PV and the difficulty 
in using one equalization function for all PV system s and vented battery designs. Many PV systems 
may not be able to reach the normally high equalization voltage and spend the required time at PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
38 © EAC 2008 — All rights reserved voltage for a complete equalization charge, but even if equalization is not complete, the additional 
charge can be beneficial. 
 
D.3 PV array to load ratio 
 
The PV array to load ratio (A:L) is the average da ily PV ampere-hours or watt-hours available divided 
by the average daily load ampere-hours or watt-hou rs. The A:L ratio is a very important PV system 
design parameter because it determines if there are sufficient charge Ah or Wh to recharge the 
battery during average solar resource periods. In low resource periods, the A:L ratio can be 
insufficient to charge the battery, and in high resource periods, it can result in excessive battery 
charging. An average daily A:L ratio of 1.3 for Ah or 1.4 for Wh can maintain the PV battery regulation 
voltage for about two to three hours every day. Some  batteries may suffer permanent capacity loss as 
a result of the low A:L ratio during low resource  periods. If battery perform ance problems arise after 
extended low resource periods, then battery recovery  can be improved by increasing the A:L ratio. 
 
D.4 Charge controllers 
 
PV charge controllers are designed to prevent exce ssive battery charging. In addition to charge 
control, PV charge controllers may include equaliz ation charge control functions, a LVD, a load 
control relay, a battery status indicator, a backu p engine generator charge control relay, a PV power 
diverter to auxiliary load, and a wiring center. PV ch arge controllers will use one of three basic charge 
control methods, which are on/off, pulse width m odulated (PWM), and constant voltage. All the above 
charge control methods will work well with vented batteries, bu t it is important to use the right 
regulation voltage for the battery and system desi gn. Typically, VRLA batteries are more easily 
charged with PWM and constant voltage charge contro l. This is because of the difficulty in obtaining 
the correct time interval between the high-voltag e disconnect and reconnect for on/off controllers. 
Rapid on/off cycling can cause the charge controller to malfunction if the reconnect voltage is too high 
or undercharge the battery if the reconnect voltage is too low. Usually, battery manufacturers do not 
provide recommended on/off set points, so determining the right set points can require some testing if 
the PV system has higher or lower than normal charge rates or has loads that operate while the PV is 
charging the battery. Generally, battery manufactu rers do provide recommended constant voltage set 
points, which are also the same as PWM set points.  D.5 V
r set point 
 
The Vr set point is the maximum voltage that a charge  controller will allow the battery to reach under 
charging conditions. At this point, the charge cont roller will either discontinue charging or begin to 
taper the charging current to the battery. Most ba ttery manufacturers will recommend constant voltage 
set points for charging their batteries in cycling applications. With vented lead-antimony batteries, 
there is considerable fl exibility with respect to Vr set point. Vr set point values for constant voltage 
charging from 2.40 V per cell to 2.45 V per cell are common and in special cases can be set up to 
2.55 V per cell depending on system and battery desi gn. Higher regulation voltages will increase 
available capacity but increase water loss. VRLA  battery designs require very precise voltage 
regulation at the battery manufacturer's recommended Vr set point. VRLA set points of 2.35 V per cell 
or 2.40 V per cell for cycle charging applications are most common. Increasing the regulation voltage 
above the manufacturer's recommended value may shorten the cycle-life of VRLA batteries due to an 
increased likelihood for venting and water loss.  
On/off controllers require two set point voltages, the array disconnect ( V
r) and the reconnect voltage 
(Vrr). In most stand-alone PV systems using vented  lead-antimony batteries, the array disconnect 
voltage should be between 2.45 and 2.50 V per cell and the array reconnect should be about 2.28 V 
per cell. The choice of the array reconnect volt age is dependent on the load profile and the switching 
speed of the PV charge controller. If there is a l oad current when the PV a rray reaches the disconnect 
voltage, then the reconnect voltage may be lowered to  accommodate the rapid drop in battery voltage 
under load. 
 
Most battery manufacturers do not recommend on/ off charging for VRLA batteries, but many PV 
systems have successfully used on/off controllers if  set points are appropriate. The key to successful 
implementation of an on/off VRLA charge controller is to set the array disconnect to about 0.02 to 
0.05 V per cell higher than the recommended constant voltage regulation voltage and set the PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  39 reconnect voltage to about 2.28 V per cell. For la rger systems, on/off staged PV array shedding is 
quite effective in providing a taper charge for VRLA  batteries. Table D.1 provides possible PV charge 
controller set points for VRLA, vented lead ca lcium, and vented lead-antimony batteries. 
 
Table D.1 — Default PV battery charge controller regulation voltages at 25 °C 
 
Variable Vented, lead
antimony a Vented, lead
calcium a VRLA, AGM a VRLA, Gela
Vr, set point, V per cell 
(Constant voltage or PWM) 2.40 to 2.50 2.45 to 2. 55 2.35 2.35 to 2.40 
Vr set point, V per cell (on/off 
disconnect) 2.45 to 2.50 2.50 to 2.55 2.40 to 2.42 2.40 to 2.42 
Vrr set point, V per cell (on/off 
reconnect) 2.25 to 2.28 2.25 to 2.28 2.25 to 2.28 2.25 to 2.28 
LVD, V per cell 1.90 to 2.00 1.90 to  2.00 1.90 to 2.00 1.90 to 2.00 
LVR, V per cell 2.17 to 2.25 2.18 to  2.25 2.18 to 2.25 2.18 to 2.25 
* This value has to be within the system's operating voltage limits. 
 
 
D.6 Maximum system voltage 
 
Many PV battery systems are nominally 48 V or less. Higher voltage battery banks are routinely 
installed and used successfully, but special care must be taken with these higher voltage battery 
systems to prevent cell imbalances, grou nd faults, and ensure electrical safety. 
 
As the number of series cells in a battery increa ses (e.g. battery strings over 48 V), it becomes 
increasingly easier for individual cells to become charge unbalanced. As a consequence, the battery's 
cells can be at various states of charge, which w ill be reflected by cells having various voltages and 
available capacities. If not corrected, any u nbalanced condition will continue to degrade with 
subsequent cycles, resulting in increasingly greater  variation in cell voltages and, more importantly; 
cell available capacities. In any case, the battery  manufacturer should be consulted for corrective 
action. One bad cell can damage the entire battery bank. To prevent this requires cell voltage 
monitoring at regular intervals and appropriate action when a bad cell is identified. There are a 
number of probable causes for battery string cell im balances that could include a weak cell, high-
resistance connection, and consistent undercha rging. If repair of the connection and/or an 
equalization charge does not recover the cell, then cell replacement is possible in some cases where 
the battery string is relatively new.  
Electrical safety at higher battery voltages requires  electrically shielding all exposed battery terminals 
and using electrical disconnects, fuses, and circ uit breakers rated for the maximum DC battery 
voltage in accordance with KS 662.  
D.7 Ground faults 
 The higher the battery voltage, the more impact exis ting battery string ground faults have on the 
system. Ground faults can result in battery fires and explosions due to the electrical heating of a 
current path to ground. Preventing ground faults requires good battery installation and maintenance 
practices. Battery maintenance includes the following: 
 — Removing corrosion and electrolyte vapor dep osits on the top surface of the battery  
 — Ensuring that there are no conductive surfaces to ground near the terminals 
 
— Using nonconductive battery trays or ca ses, particularly for systems over 48 V 
 — Using appropriate battery vent caps with flame ar resters to minimize the possibility of fire and/or 
explosions 
 Ensuring adequate standoff or separation between ba ttery terminals and grounded support structures 
is critical. Electrolyte mist will depo sit on battery surfaces, reducing th e electrical resistance to ground. 
If electrically conductive and grounded battery trays are used with vented cells, then the possibility of PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
40 © EAC 2008 — All rights reserved ground faults is greatly increa sed. Conductive cases are prohib ited for vented lead-acid battery 
systems operating above a nominal 48 V (24, 2 V cells). Conductive racks may be used for these 
systems provided no rack material is wi thin 150 mm of the tops of the cells. 
 
For VRLA batteries, the conductive electrolyte is well contained within the battery and usually does 
not form on the battery surface. The improved elec trolyte containment allows VRLA batteries to be 
used in conductive trays or racks over 48 V. VRLA  batteries do leak electrolyte on occasion, so every 
effort should be made to keep these batteries clean and minimize electrically conductive support 
structures near the battery term inals. In many higher voltage battery banks, ground fault detection 
equipment is an important safety f eature that can warn personnel when excessive leakage currents 
are occurring and a ground fault is pending.   
D.8 Depth of discharge 
 Depth of discharge (DOD) is the percentage of discharged Ah per cycle relative to rated battery 
capacity. Most applications only cycle the battery to a maximum of 80 % DOD or less. PV systems will 
usually cycle the batteries daily between 10 % and 20 %, but in low solar resource periods, the 
battery may cycle to the LVD. LVD is usually set between 1.9 V per cell and 2.0 V per cell for 
discharge rates higher than the 35 h rate. The above LVD set points will discharge the battery between 50% and 95% DOD. It is also important to  adjust the LVD voltage upw ard to prevent over 
discharge if discharge rates are much lower. 
 D.9 Temperature effects  
PV systems are installed all around the world in hot an d cold climates, and as a result of these climate 
variations, batteries in these systems need to be cared for appropriately. It is unlikely that PV batteries 
will be installed in systems where there is extra power for heating and air conditioning, so some 
battery temperature extremes are unavoidable. If the battery temperature deviates from 25 °C 
significantly, temperature-compensated regulati on voltage is a recommended feature of the PV 
charge controller. Additional cost-effective meas ures for battery temperature management include 
insulating the battery enclosure, partially or comp letely burying the battery enclosure, and ensuring 
that the battery or enclosure is not exposed to direct  sunlight or cold drafts. It is also important to 
understand that VRLA batteries are much more sensitiv e to temperatures over 25 °C. Many times just 
using a more heat-tolerant battery such as a vent ed lead-antimony battery is a good solution to the 
potential cycle-life limiting effects of higher oper ating temperatures on VRLA batteries. Vented lead-
acid batteries can be operated at temperatures between -10 °C and 40 °C, but every effort should be 
made to maintain battery temperature near 25 °C when possible. This prevents freezing of the 
electrolyte, excessive grid corrosion and improves  performance. VRLA batteries, on the other hand, 
are much more tolerant to cold temperatures becaus e if the electrolyte freezes , it is unlikely to crack 
the battery case, but at temperatures near 35 °C , VRLA batteries are near their recommended high 
temperature limit. 
 D.10 Autonomy  
Autonomy is the number of days a PV battery will carry  the load without energy from the PV array. 
The number of days of autonomy is a function of the acceptable loss of load probability and the 
weather patterns. Although many stand-alone PV systems are designed with five days of autonomy, 
some critical load systems (e.g., telecommunication) feature batteries with ten or more days of autonomy. Typical autonomies range from 5 to 25 days . Several factors go into this design guideline, 
including the length of typical cloudy periods and t he practical limits for system component sizing. Low 
insolation days in locations where PV is used will usually last less than five days. Excessive autonomy can make it difficult to charge the battery and ca n increase system cost wi th an oversized battery 
 
D.11 Geographical site location  
Geographical site location issues generally include weather patterns, minimum and maximum 
temperatures, and earthquake zones. If the weather  patterns are such that there are seasonal 
patterns of low solar resource, then the load may have to be disconnected or greatly reduced during 
that time period. In very cold or very hot clim ates, the batteries should be insulated or installed PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-1:2003  
© EAC 2008 — All rights reserved  41 underground to protect them from extreme temperat ures. In earthquake zones, the batteries need 
adequate support as required by the local building codes. 
 
D.12 PV battery end-of-life 
 
In stationary float service applications, battery end -of life is generally defined when battery capacity 
drops to less than 80 % of its rated value. If this requirement was applied to standalone PV systems, 
many batteries would be at end-of life shortly after in stallation. End-of life for PV batteries is not well 
defined. In most stand-alone PV applications, the batte ry end-of life is defined when the battery fails 
to meet the daily loads of the sy stem during good solar resource periods. Battery failure can be due to 
undercharging, excessive loads, sy stem component failures, or normal battery wears out. Excessive 
loads and/or system component failures will usually re sult in undercharged batteries with associated 
capacity loss. If the battery is continually underchar ged, then "hard" sulfatio n, stratification, negative 
plate grid loss, and other degradation mechanisms in t he positive active mass will result in permanent 
premature capacity losses. Battery recovery after continued under charging may or may not be 
possible by equalization. Normal wear out also results in capacity loss from the traditional 
mechanisms of positive grid corrosion and positive active material shedding. When this occurs, the 
battery can experience excessive positive plate growth or bulging and cell shorting. 
 
 
  
 
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© EAC 2008 — All rights reserved