Conference Paper

NREL/CP-540-42240

July 2009

Battery Requirements for Plug-In 

Hybrid Electric Vehicles – 

Analysis and Rationale 

A.A. Pesaran and T. Markel

National Renewable Energy Laboratory

H.S. Tataria

General Motors Corporation

D. Howell

U.S. Department of Energy

Presented at the 23rd International Electric Vehicle Symposium 

(EVS-23) 

Anaheim, California

December 2–5, 2007
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1 

Battery Requirements for Plug-In Hybrid Electric Vehicles – 

Analysis and Rationale 

AHMAD A. PESARAN and TONY MARKEL

National Renewable Energy Laboratory 

1617 Cole Blvd., Golden, CO 80401 USA 

Principal Engineer, Tel: +1 303 275-4441; Fax: +1 303 275-4415; ahmad.pesaran@nrel.gov

Senior Engineer, Tel: +1 303 275-4478; Fax: +1 303 275-4415; tony.markel@nrel.gov

HARSHAD S. TATARIA

USABC and FreedomCAR Program Manager

General Motors Corporation

30001 Van Dyke Ave., MC 480-210-427, Warren, MI 48092 USA

Tel: +1 586-575-3472; Fax: +1 586-492-6645; harshad.s.tataria@gm.com

DAVID HOWELL 

Energy Storage R&D, Vehicle Technologies Program 

U.S. Department of Energy

EE-2G, 1000 Independence Ave., S.W., Washington, DC, 20585 USA

Tel: +1 202-586-3148; Fax: +1 202-586-2476; david.howell@ee.doe.gov 

Abstract

Plug-in hybrid electric vehicles (PHEVs) have the potential to displace a significant amount of petroleum 

in the next 10 to 20 years. The main barriers to the commercialization of PHEVs are the cost, safety, and 

life of batteries. Therefore, the U.S. Department of Energy and auto companies have embarked on a 

program to develop batteries for PHEVs. Defining battery targets or requirements to benchmark progress

is essential. In support of the U.S. Advanced Battery Consortium (USABC), vehicle analysis and battery 

sizing studies were performed to recommend battery requirements. The analysis process included 

defining vehicle platforms, vehicle performance targets, the desired equivalent electric range operating 

strategy (all electric or blended), and the state-of-charge window. Based on the analysis, USABC

members recommended two categories of batteries: one for a 10-mile equivalent electric vehicle (EV) 

range (high power/energy ratio) and one for a 40-mile EV range (high energy/power ratio). Four sets of 

requirements were defined: (1) system-level (range pack cost, calendar life, volume, weight, and energy 

efficiency); (2) charge-depleting hybrid EV (HEV) mode (2-second and 10-second discharge power, 10-

second regenerative braking power, available energy at constant power, number of deep cycles, maximum

recharge rate); (3) charge-sustaining HEV mode (available energy for charge-sustaining operation, cold 

cranking power, number of shallow charge-sustaining cycles); and (4) battery limits (maximum current, 

maximum and minimum voltage, operating and survival temperatures). In this paper, we present the 

assumptions, the analysis, discussions, and the resulting requirements adopted by USABC.

Keywords: Plug-in hybrid electric vehicles, PHEV, battery, EV range, charge-depleting

1. Introduction

A plug-in hybrid electric vehicle (PHEV) is a hybrid electric vehicle (HEV) with the ability to recharge 

its energy storage system with electricity from an off-board power source such as a grid. The key 

advantage of PHEV technology relative to hybrid electric and conventional vehicles is fuel flexibility. A 

PHEV uses stored electrical energy to propel the vehicle and reduce petroleum consumption by the 
2 

combustion engine. This provides an opportunity to drive primarily in electric mode and reduce emissions 

in congested cities around the world. 

A study by Simpson estimates that a PHEV with usable electrical energy storage equivalent to 20 miles of 

electric travel (PHEV20) would reduce petroleum consumption by 45% relative to that of a comparable 

conventional combustion engine vehicle [1]. Plug-in hybrid electric vehicles have the potential to displace 

a significant amount of petroleum in the next 10 to 20 years. Many believe that PHEVs could enter the 

passenger vehicle market much sooner than hydrogen fuel cell vehicles, since there is no need for a costly 

hydrogen fueling infrastructure and there are fewer technical barriers. As a result, a significant amount of 

activity has been initiated to advance the development of PHEVs and batteries suitable for them. For 

example, the U.S. Department of Energy’s (DOE) Vehicle Technologies Program (which includes the 

FreedomCAR and Fuel Partnership) has developed a research and development (R&D) plan to evaluate 

the potential of PHEVs, and the program has proposed R&D activities to improve the batteries and power 

electronics that go into PHEVS while also improving vehicle efficiency technologies [2]. 

The chief barrier to the commercialization of PHEVs has been identified to be the battery, in terms of

cost, combined shallow/deep cycle life, calendar life, volume, and safety. Therefore, DOE and U.S. auto 

companies, through the U.S. Advanced Battery Consortium (USABC), have embarked on a sizable 

program to develop batteries for PHEVs. Such a program needs to have battery targets or requirements to 

benchmark progress. In support of USABC, we have performed vehicle analysis and battery sizing studies 

to recommend battery requirements. USABC intends to use these requirements in soliciting proposals 

from potential battery developers.

The National Renewable Energy Laboratory (NREL) and Argonne National Laboratory (ANL) have 

conducted a number of analyses to help define these battery requirements. Researchers at ANL developed 

a battery model and a process for performing analyses for sizing energy storage systems for plug-in 

applications and investigated the impacts of all-electric range, drive cycle, and control strategy [3]. NREL 

researchers performed simulations to investigate the impacts of component sizes (engine power, motor 

power, and battery power and energy) in meeting performance constraints and energy consumption 

characteristics of vehicles over different driving profiles as a function of the equivalent electric range 

capability and the degree of hybridization [4, 5]. NREL also investigated component costs and impacts on 

benefits [1]. 

These definitions and terminologies will be helpful in the discussion that follows: 

• Charge-depleting (CD) mode: An operating mode in which the energy storage state-of-charge 

(SOC) may fluctuate but, on average, decreases while the vehicle is driven. 

• Charge-sustaining (CS) mode: An operating mode in which the energy storage SOC may 

fluctuate but, on average, is maintained at a certain level while the vehicle is driven. This is the 

common operating mode of commercial hybrids such as the Ford Escape hybrid, the Toyota 

Prius, the Chevy Tahoe hybrid, and the Dodge Durango hybrid. 

• All-electric range (AER): After a full recharge, the total miles driven electrically (with the 

combustion engine off) before the engine turns on for the first time.

• Blended or charge-depleting hybrid (CDH) mode: An operating mode in which the energy 

storage SOC decreases, on average, while the vehicle is driven; the engine is used occasionally to 

support power requests.

• Zero-emission vehicle (ZEV) range: The same as the all-electric range (AER); there are no 

tailpipe emissions when the vehicle is in EV mode. 

As part of the process of defining battery requirements, the USABC formed a PHEV Battery Work

Group. As members of this Work Group, we obtained input from a number of organizations, engaged in 

discussions, made some assumptions for vehicle and expected performance attributes, and performed
3 

analyses. The results of the analysis were discussed in the Work Group and reported back to USABC and 

FreedomCAR Technical Teams (including Vehicle System Analysis) for guidance. Based on the 

discussions, questions, and feedback, we looked at the impact of battery and range assumptions as well as

different strategies, drive cycles, and vehicle attributes. In this paper, we present the rationale behind 

selecting the assumptions, performing the analyses, and the resulting requirements.

2. Approach for Power and Energy

From previous analyses, it was understood that the energy storage requirements for PHEVs depend on the 

vehicle platform, vehicle performance, hybrid configuration, drive cycle, electric range, operating 

strategy, all-electric range capability, and level of electric performance on various drive cycles. The 

requirements were not intended to be specific nor to depend on a particular control strategy. Rather, they 

intended to be flexible enough to allow them to be applied to different vehicles and operating strategies. 

The analysis process included defining vehicle platforms (mass, aerodynamic, and rolling resistance); 

vehicle performance targets (acceleration, top speed, grade); the desired equivalent electric range (10−60 

miles); the operating strategy (all-electric and blended); and the usable SOC window. The analysis 

(including vehicle simulations and power/energy calculations) provided electric vehicle consumption 

(Wh/mile), peak power requirements for a particular drive cycle, and peak power requirements during

charge-sustaining operation. 

2.1 Vehicle Assumptions

The choice of a vehicle platform and performance characteristics strongly impacts component sizing and 

battery requirements. Cars make up a significant portion of the light-duty vehicle market, and midsize 

cars represent a large portion of the car market, so to represent this segment we studied a midsize car, 

similar to a Chevy Malibu. Another large portion of the light-duty vehicle market is captured by sport 

utility vehicles (SUVs), so a midsize SUV similar to the Ford Explorer was investigated. SUVs are 

popular with U.S. drivers, so it was important to consider a plug-in for this market segment. SUVs also 

consume more fuel than cars, so there is a greater opportunity to save petroleum with plug-in hybrid 

SUVs; however, the higher cost and volume differential were concerns. Because of the growing interest 

among U.S. consumers in crossover utility vehicles (UVs) (a vehicle somewhere between a traditional 

SUV and a car), a midsize crossover UV, similar to the Chrysler Pacifico, was also studied. 

Research included several iterations on the mass, frontal area, rolling resistance, and aerodynamic drag 

coefficient. Table 1 shows the typical vehicle assumptions (midpoints) that were used for the requirement 

analysis and recommendations. A reasonable sensitivity around each parameter was considered and 

presented in [3]. The vehicle performance targets, selected based on today’s vehicle performance and 

future trends, are given in Table 2.

Table 1. Vehicle assumptions used for simulations and component sizing

Parameter Units Midsize 

Car

Midsize 

Crossover UV

Midsize 

SUV

Approximate Glider Mass kg 940 1100 1200

Approximate Vehicle Test Mass kg 1600 1950 2000

Frontal Area m2 2.22 2.69 2.89

Drag Coefficient 0.308 0.417 0.42

Rolling Resistance 0.009 0.010 0.011 

Accessory Electrical Load W 800 1000 1200
4 

Table 2. Vehicle performance parameters

Parameter Value

Acceleration from 0 to 60 mph 9 s

Top Speed 100 mph

Grade at 55 mph 6%

2.2 Vehicle Simulations and Analysis

We used vehicle simulations (ANL’s Powertrain Simulation Toolkit, or PSAT) and power flow 

calculations to size the various components, including the battery, engine, and motor. Component sizes 

were selected to satisfy the performance constraints listed in Table 2 for each of the vehicles identified in 

Table 1. Each vehicle’s gasoline and electricity consumption over various driving cycles were calculated 

based on the model output. The vehicle’s performance and energy use were coupled to vehicle mass, so 

the model was able to capture mass compounding in the sizing of components. PSAT simulations were 

completed using an electric vehicle model with a five-speed transmission and with slightly oversized 

power and energy inputs to a generic battery model. Spreadsheet calculations were used to determine the 

vehicle test mass for the simulations (accounting for variations in the mass of the engine and batteries to 

satisfy vehicle requirements). 

The required electric drive sizing was based on completing the given distance of Urban Dynamometer 

Driving Schedule (UDDS) drive cycle repetitions all electrically while limiting the battery energy 

utilization to 60%−70% of the “available” total. Beginning battery power and energy were assumed to be 

oversized by 30% and 20%, respectively, to account for degradation over the life of the vehicle [6]. 

However, this was used only in estimating the initial mass of the battery pack, and thus the vehicle, for 

calculating fuel and electricity consumption. The useful SOC range and degradation factors were not 

defined in requirements since they are technology-specific and should be specified by battery suppliers. 

The required engine sizing was based on meeting a 6% grade requirement at 55 mph and two-thirds of 

peak power [6]. Iterations were performed to incorporate mass-compounding interactions between the 

component sizing and vehicle requirements. 

2.3 PHEV Design Strategy

The PHEV Battery Work Group discussed the advantages and disadvantages of all-electric and blended 

operations and their impact on the size and cost of the energy storage system. In all-electric mode, the 

motor and energy storage provide all the power needed to move the vehicle. The power requirements 

depend on the drive cycle and the amplitude and duration of peak power, and the required energy depends 

on the distance driven on that drive cycle. With more aggressive cycles, the power requirements increase 

and the energy needed to drive the same distance also increases. In blended mode, the motor provides 

most of the power to move the vehicle, while the engine provides assist for peak pulses that are beyond 

the capability of the motor/energy-storage system. As a result, the power capability of the energy-storage 

system could be lower in blended operation; however, it could also be of longer duration, as shown by

Markel [4]. 

The all-electric mode has the advantage of displacing more gasoline and reducing more vehicle 

emissions; however, aggressive drive cycles and longer electric ranges require larger and costlier energystorage systems. To qualify for ZEV or Advanced Technology Partial ZEV (AT PZEV) credits, the

California Air Resource Board (CARB) requires the minimum AER to be 10 miles during the UDDS 

drive cycle. The Work Group felt it was important for a PHEV to qualify for AT PZEV credits and 
5 

recommended using the UDDS drive cycle in identifying the power and energy requirements for the allelectric mode. This meant that, during actual daily driving profiles that are more aggressive than UDDS, 

the vehicle would operate in blended mode with the engine turning on to provide an assist to the electric 

drive system during high-power peak demands. Real-world blended operation decreases the gasoline fuel 

economy and increases tailpipe emissions slightly, but it would keep the energy storage size and cost 

manageable. Note that the analysis showed that the energy needed to drive the equivalent electric range in 

either AER or blended mode is about the same. 

3. Analysis Results for Power and Energy

The results of simulations for the platforms, range, strategy, and performance matrix are presented in 

Figures 1 and 2. These and other analysis results indicate the following: 

• Increased vehicle mass leads to increased peak power and stored electrical energy requirements. 

• Peak power was higher for the SUV studied than it was for the crossover UV, which in turn had a 

higher peak power than the car did. 

• The electric energy consumption for propelling the vehicle a given distance over the UDDS drive 

cycle (Wh/mile) does not significantly depend on whether the operation is all-electric or blended. 

• Electric energy consumption strongly depends on the vehicle platform and efficiency of the 

electric components; the energy consumption of the SUV was higher than that of the crossover 

UV, which in turn was higher than that of the car. 

• Required motor/battery peak power (2-second) for all-electric operation is higher than the 

motor/battery peak power (10-second) for blended operation. The reason for the difference in 

duration of peaks is an artifact of the UDDS driving profile and the associated power need. 

0

50

100

150

200

250

300

350

400

450

500

car 10 AERcar 40 AER

car 10 CDHcar 40 CDH

cross 10 AERcross 40 AER

cross 10 CDH cross 40 CDH

SUV 10 AER

SUV 40 AER

SUV 10 CDH

SUV 40 CDH

Vehicle Consumption (Wh/mi)

AER: All Electric Range Mode

CDH: Blended or Charge Depleting Hybrid Mode

Figure 1. Electric energy consumed per mile for various vehicles and operating modes

For the simulation in Figures 1 and 2, it was assumed that the blended or CDH peak was about 50% of the 

AER peak power. Markel [4] has indicated that more than 85% of an AER fuel consumption reduction 
6 

could be achieved at this power level. Consumption reductions drop more dramatically as peak power is 

reduced. The 50% value provided a balance between power reduction (battery size) and consumption 

goals.

0

10

20

30

40

50

60

70

80

car 10 AER

car 40 AER

car 10 CDHcar 40 CDH

cross 10 AERcross 40 AER

cross 10 CDH cross 40 CDH

SUV 10 AERSUV 40 AER

SUV 10 CDHSUV 40 CDH

EOL Discharge Power (kW)

Power Pulse Duration

AER cases are 2s

CDH cases are >10s

AER: All Electric Range Mode

CDH: Blended or Charge Depleting Hybrid Mode

 Figure 2. Peak power needed for various vehicles and operating modes over the UDDS drive cycle

The analysis showed that the midsize car consumed about 280-290 Whr/mile, the midsize crossover used 

about 340 Wh/mile, and the midsize SUV consumed about 420 Wh/mile. An example of the analysis 

results is shown in Table 3, generated by Gonder [6] for the PHEV Battery Work Group. The table shows 

specific numbers for electric range and pulse discharge power over the UDDS drive cycle and maximum

regenerative braking (regen) pulse based on the US06 drive cycle for the crossover platform. Note that the 

(2-s) power to (available) energy ratio (P/E) decreases with an increase in the electric range for the same 

class of vehicle. P/E increases with the mass of the vehicle for the same electric range. Power-assist 

HEVs have batteries with a P/E ratio of more than 15 to 20; batteries for electric vehicles have a P/E ratio 

of less than 2 to 3.

Table 3. Results of simulations for midsize crossover UV [6]

Characteristics Units 10 Miles 

AER

20 Miles 

AER

40 Miles 

AER

Pulse Discharge Power (2 s), UDDS kW 50 51 54 

Pulse Discharge Power (10 s)* kW 37 39 40 

Max Regen Pulse (2 s), US06 kW 36 37 39 

Max Regen Pulse (10 s)* kW 27 28 29 2

Available Energy for CD Mode kWh 3.36 6.7 13.9 

Electrical Energy Consumption Wh/mile 336 340 348

(discharge 2 s) Power / (available) Energy Ratio W/Wh 14.9 7.6 3.9

*The 10-second pulse is 75% of the 2-second pulse representing state-of-the-art high-energy lithium ion cells. 
7 

4. Selection of Battery Requirements

4.1 Power and Energy for the Charge-Depleting AER Mode

Following discussions of the results of the analysis with the Work Group, FreedomCAR Tech Teams, and 

the USABC, two sets of requirements for two types of batteries were selected: one with a high 

power/energy ratio for larger vehicles, such as a crossover UV, and one with a high energy/power ratio

for midsize cars. Having more than two sets of targets and requirements would have created an 

unnecessary burden and confusion for all involved in the development, evaluation, and testing of the 

batteries. These two sets of battery requirements could cover the majority of batteries for various types of 

PHEVs. In addition, for the mid-term (by 2012), the targets are more achievable for batteries in vehicles 

with a 10-mile AER [the minimum range for obtaining the CARB Advanced Technology-Partial ZeroEmission Vehicle (AT-PZEV) credits]. 

The crossover vehicle platform and associated power and energy requirements were found to be valuable 

and feasible for the mid-term, 10-mile AER pathway (high P/E ratio battery). The initial incremental cost 

of the battery and the PHEV when compared with fuel savings (even with gasoline at $3/gallon) did not 

justify the higher AERs and other vehicle scenarios. The mid-term, 10-mile batteries have requirements 

similar to the batteries for power-assist HEVs that USABC developers are already working on. So power, 

energy, and cost requirements for mid-term were believed to be more achievable. For the long-term 

(2016), the battery targets were selected to be more challenging with a 40-mile AER to meet the range 

stated in President Bush’s 2006 State of the Union Address. The Wh/mile and peak power characteristics

of the midsize car were found to be more attractive for the long-term, 40-mile AER (high E/P battery). 

For the high power/energy case (mid-term, 10 mile AER), the vehicle energy consumption assumed was 

340 Wh/mile, and the 2-second peak power discharge assumed was 50 kW. The 10-second discharge and 

regen powers for this case were 45 kW and 30 kW, respectively. Therefore, for the 10-mile AER, the 

available energy needed was 3.4 kWh. For the high energy/power case (long-term, 40-mile AER), the 

vehicle energy consumption was assumed to be 290 Wh/mile, and the 2-second peak power discharge was 

set to 46 kW. The 10-second discharge and regen powers for this case were 38 kW and 25 kW, 

respectively. Therefore, for the 40-mile AER, the available energy needed was 11.6 kWh. Note that the 

selection of these values was based on the results of the analysis and on input from car company 

representatives who have significant experience with the operation of HEVs and EVs. At times the values 

were increased to err on the conservative side. The power capabilities of the batteries must be provided 

over the entire range of the SOC in which the operation is expected to be AER.

Two questions came up for setting the energy requirements:

1. At what rate should the battery be discharged during the CD mode? 

2. What should the SOC window be for the battery?

The responses to those questions were as follows: 

1. The rate should be 10 kW (roughly one-fourth of peak power), which approximates the power 

needed to propel either of the vehicles at a constant speed of 25 to 30 mph. 

2. The SOC window was left to the battery developer or supplier to decide, based on the limits 

of the technology considering the trade-off between weight and life. However, in most of the 

Work Group discussions, a 70% SOC window was assumed.

Table 4 summarizes the power and energy requirements. Note that a battery must meet these requirements 

at 30°C and at the end of life (EOL), which is discussed later. This means that the battery 

developer/supplier has to set a margin for the beginning of life to account for battery degradation, or fade 
8 

in energy and power. This is usually about 20% or 30%, but it was left to the developer/supplier since 

each technology can be different. USABC has used a standard temperature of 30°C for other HEV and 

EV battery life requirements. 

Table 4. PHEV power and energy requirements (at 30°C) for two battery categories

Characteristics at EOL (End of Life) Units 

High 

Power/Energy 

Ratio Battery

High 

Energy/Power 

Ratio Battery

Technology Readiness Target year 2012 2016

Reference Equivalent Electric Range miles 10 40

Peak Pulse Discharge Power - 2 s kW 50 46

Peak Pulse Discharge Power - 10 s kW 45 38

Peak Regen Pulse Power - 10 s kW 30 25

Available Energy for CD (Charge Depleting) Mode, 10 kW Rate kWh 3.4 11.6

4.2 Battery Power and Energy for the Charge-Sustaining HEV Mode

A PHEV operates like an HEV when the battery is depleted, that is, discharged to a certain SOC. Most 

HEVs operate in a charge-sustaining mode around a predefined SOC. During CS HEV operation, the 

battery has to meet the discharge and regen power with available energy around this SOC. USABC and

the FreedomCAR partnership have previously set battery requirements and targets for charge-sustaining 

power-assist HEVs [7]. For a minimum power-assist HEV, the targets are 25 kW 10-second discharge

and 20 kW 10-second regen with 300 Wh available energy at 30°C. For a maximum power-assist HEV, 

the targets are 40 kW 10-second discharge and 35 kW 10-second regen with 500 Wh available energy at 

30°C. The AER power requirements for the 10-mile and 40-mile ranges discussed above are higher than 

the targets set for maximum and minimum power-assist HEVs, respectively. 

After looking at the power capabilities of tested lithium-ion batteries at various SOCs, the Work Group

determined that if a battery system meets the AER peak power targets, it also would meet the CS HEV 

needs, so no additional peak power target for a CS HEV was selected. The available energy requirements 

for the CS HEV mode were selected to be 500 Wh for a 10-mile (high P/E ratio) battery (the same as 

maximum power-assist) and 300 Wh for a 40-mile (high E/P ratio) battery. The total EOL energy is the 

available energy/SOC window and depends on the battery technology.

For setting cold cranking power requirements, the following scenario was assumed: the PHEV is driven 

in CS HEV mode (SOC at lowest nominal CD value) in the last part of a trip and then parked without 

being plugged into the grid. The vehicle is kept at -30°C for a few days so the internal temperature of the 

batteries reached -30°C. In this scenario, the vehicle will be started as a CS HEV at -30°C, so the battery 

should support the engine cranking. This scenario is considered the worst for cold cranking since, if the 

battery is plugged in or at higher SOC, then the cold cranking capability of the battery would be higher. 

The USABC cold cranking power requirements of a maximum power-assist HEV at -30°C is three 2-

second, 7 kW pulses with a 10-second rest between each pulse. The same cold cranking power 

requirements were selected for both the PHEV battery categories. The purpose of cold cranking is to be 

able to start the engine at worst conditions.

Table 5 summarizes the cold cranking power and available energy requirements for the CS HEV mode at 

end of life. 
9 

Table 5. PHEV available energy and cold cranking power requirements for the CS HEV mode

Characteristics at EOL (End of Life) Units 

High 

Power/Energy 

Ratio Battery

High 

Energy/Power 

Ratio Battery

Available Energy for CS (Charge Sustaining) Mode kWh 0.5 0.3

Cold Cranking Power at -30°C, 2 s, 3 pulses (10 s rest between) kW 7 7

4.3 Calendar and Cycle Life 

The USABC/FreedomCAR calendar life target for power-assist HEVs is 15 years [7]. This is a research 

target based on the expected average life of passenger cars, which is around 14 years. The same calendar 

life was selected for PHEVs for either battery type. However, since the PHEV battery gets plugged in and 

is fully charged often, its temperature may be generally higher than that of the HEV battery over its life; 

so 35°C was selected as the temperature for measuring the calendar life of PHEV batteries, versus 30°C 

for HEV batteries. 

The cycle life for the CS HEV mode of PHEV for both high P/E and high E/P batteries was selected to be 

the same as maximum power-assist HEVs, as defined by USABC/FreedomCAR, which is 300,000 cycles 

of 50 Wh profile. This is equivalent to about 150,000 miles (the life expectancy of emission control 

devices set by CARB). For CD HEV operation, it was assumed that both 10-mile and 40-mile batteries 

are deep-discharged once a day—charged fully at the beginning of the day to the maximum SOC, 

according to the battery supplier, and discharged fully to the minimum SOC, according to the supplier. 

The number of deep discharges was calculated using 1 cycle per day, 330 days per year - accounting for 

some weekends with no deep discharging - and 15 years per battery, or about 5000 CD cycles. The CD 

discharge energy throughput was calculated using the number of deep discharges multiplied by the CD 

available energy: 5000*3.4 kWh = 17 MWh for the 10-mile battery and 5000*11.6 kWh = 58 MWh for 

the 40-mile battery. Table 6 provides a summary of calendar and cycle life requirements.

Table 6. Calendar and cycle life requirements for PHEV batteries

Characteristics at EOL (End of Life) Units

High 

Power/Energy 

Ratio Battery

High 

Energy/Power 

Ratio Battery

Calendar Life, 35°C year 15 15

Charge Depleting (CD) Cycle Life cycles 5,000 5,000

Discharge Throughput Energy through CD Cycles MWh 17 58

CS HEV Cycle Life, 50 Wh Profile cycles 300,000 300,000

4.4 System-Level Requirements 

Price. A reasonable battery system cost is critical to the success of PHEVs. Although, as with HEVs, 

early adaptors of the technology could be willing to pay higher prices for PHEVs, for mass-market 

penetration the initial incremental cost of a PHEV should be offset by savings on gasoline costs in a 

reasonable amount of time. The price targets selected for the battery system were set to be very 

challenging to push the technology. The battery system price target (cells, packaging, electronics, and 

thermal control) was set to $1,700 for the 10-mile (high P/E) battery and $3,400 for the 40-mile (high 

E/P) battery. The battery cost targets reflect the mid- and long-term R&D cost goals of 

$500/(available)kWh in 2012 and $300/(available) kWh in 2016. The production volume for the target
10 

system price is 100,000 units per year. In terms of price per EOL total energy, this corresponds to 

$305/kWh for the mid-term, 10-mile battery and about $200/kWh for the long-term, 40-mile battery. A 

70% SOC window was assumed. Currently, high-energy batteries cost from $800/kWh to $1,000/kWh. 

Volume and Mass. The battery system must fit in the vehicle with minimum adverse impact on the cabin 

or cargo space. Loss of cabin and cargo space could dissuade potential buyers of PHEVs from purchasing 

them, so it must be kept to a minimum. The maximum volume selected as targets were 40 liters for the

10-mile battery and 80 liters for the 40-mile battery. Assuming 70% for the SOC range and 20% for the

fade factor, these correspond to roughly 145 Wh/liter for the 10-mile battery and 250 Wh/liter for the 40-

mile battery, all at beginning of life (BOL). The mass of the battery system should be small enough to not 

have an adverse impact on the fuel economy and structure of the vehicle. The maximum weight selected 

as targets were 60 kg for the 10-mile battery and 120 kg for the 40-mile battery. These correspond to 95

Wh/kg for the 10-mile battery and 165 Wh/kg for the 40-mile battery, all at BOL. The mass and volume 

of cells, structure, packaging, electronics, and thermal control are included in the system mass and 

volume. These goals are very challenging, particularly the ones for long-term, 40-mile, high E/P ratio 

batteries. 

Recharge Rate. To recharge the battery, the Work Group considered the time to recharge the battery and 

the availability of grid power. Charging overnight in 10 hours or less seemed reasonable. According to a 

Southern California Edison (SCE) Work Group member, the nominal distribution voltage for U.S. 

residential buildings is standardized at 240 VAC, resulting in a typical residential receptacle to be rated 

for 120 VAC (line to neutral). Normally, during the generation and distribution of electricity, there are 

natural losses in the system. Hence, most U.S. utilities guarantee their voltage at 120 +/- 5%, or between 

114 V and 126 V. In some instances, depending on the location, some utilities may in fact set their 

tolerance to +/- 10%, or between 108 V and 139 V. Household receptacles in residential housing are rated 

for 15 A. Using outlets with power ratings of 120 V/20 A or 220 V/20 A increases the cost of installation, 

so they were not deemed desirable. In the United States, according to the National Electrical Code, the 

continuous power rating of an electrical outlet is 80% of the name plate, so the maximum recharge rate 

was set to 80% of 15 A. With nominal line at 120 VAC, the power was 1440 VA, or about 1.4 kW. 

System Efficiency. The battery system should be of relatively high efficiency so that the vehicle 

powertrain efficiency, and thus energy consumption, will be low. Similar to the power-assist HEV, we 

selected a minimum round-trip battery system efficiency of 90% over the USABC HEV efficiency cycle. 

The system-level requirements are summarize in Table 7. 

Table 7. PHEV battery system-level requirements

Characteristics at EOL (End of Life) Units

High 

Power/Energy 

Ratio Battery

High 

Energy/Power 

Ratio Battery

Maximum System Production Price @ 100,000 units/year $ $1,700 $3,400

Maximum System Weight kg 60 120

Maximum System Volume liter 40 80

System Recharge Rate at 30°C kW 1.4 (120 V/15 A) 1.4 (120 V/15 A)

Minimum Round-trip Energy Efficiency (USABC HEV Cycle) % 90 90

4.5 System-Level Limits 

Voltage and Current. In order to integrate the battery system with other electrical components in electric 

drive systems (motors, converters), the maximum battery voltage was set at less than 400 V, the minimum 
11 

Characteristics at EOL (End of Life) High Power/Energy Ratio 

Battery High Energy/Power Ratio Battery

Technology Readiness Target year 2012 2016

Reference Equivalent Electric Range miles 10 40

Maximum System Production Price @ 100,000 units/year $ $1,700 $3,400

Calendar Life, 35°C year 15 15

Maximum System Weight kg 60 120

Maximum System Volume liter 40 80

Peak Pulse Discharge Power - 2 s / 10 s kW 50/ 45 46/ 38

Peak Regen Pulse Power (10 s) kW 30 25

Available Energy for CD (Charge Depleting) Mode, 10 kW Rate kWh 3.4 11.6

CD Life / Discharge Throughput cycles/MWh 5,000 / 17 5,000 / 58

System Recharge Rate at 30°C kW 1.4 (120V/15A) 1.4 (120V/15A)

Available Energy for CS (Charge Sustaining) Mode kWh 0.5 0.3

Minimum Round-trip Energy Efficiency (USABC HEV Cycle) % 90 90

Cold Cranking Power at -30°C, 2 s - 3 pulses (10 s rest between) kW 7 7

CS HEV Cycle Life, 50 Wh Profile cycles 300,000 300,000

Maximum Operating Voltage Vdc 400 400

Minimum Operating Voltage Vdc >0.55 x Vmax >0.55 x Vmax

Maximum Self-Discharge Wh/day 50 50

Unassisted Operating & Charging Temperature Range °C -30 to +52 -30 to +52

Survival Temperature Range °C -46 to +66 -46 to +66

voltage at 55% of maximum voltage, and the maximum current at 300 A. These are similar to targets for 

power-assist HEVs.

Maximum Self-Discharge Rate. In order to ensure that the high-voltage battery has sufficient energy and 

power for CS HEV operation after a long parking period (normally 30 days) without being connected to a 

plug, the maximum self-discharge rate was set at 50 Wh/day (at 30°C). 

Temperatures. The unassisted operating and charging temperature range for the vehicle, and thus the 

battery, was set to between -30°C and +52°C. This is where most vehicles in the United States will 

operate. The survival (nonoperating) temperature range was set to between -46°C and +66°C. These are 

similar to those set for power-assist HEV batteries.

Table 8 summarizes the system-level limits for PHEV energy storage.

Table 8. System-level limits for PHEV batteries

Characteristics at EOL (End of Life) Units

High 

Power/Energy 

Ratio Battery

High 

Energy/Power 

Ratio Battery

Max. Current (10 sec pulse) A 300 300

Maximum Operating Voltage Vdc 400 400

Minimum Operating Voltage Vdc >0.55 x Vmax >0.55 x Vmax

Maximum Self-Discharge Wh/day 50 50

Unassisted Operating & Charging Temperature Range °C -30 to +52 -30 to +52

Survival Temperature Range °C -46 to +66 -46 to +66

4.6 Combined Requirements

Table 9 summarizes the combined set of battery requirements from Tables 4 through 8. Note that all 

requirements/targets must be met at the same time. Table 9 is organized in four categories: system level, 

CD HEV mode, CS HEV mode, and battery system limits. 

Table 9. Battery requirements for PHEVs – organized in four categories
12 

In addition to these requirements, the Work Group also set performance requirements for battery power at 

various temperatures, similar to those set for power-assist HEVs. Table 10 identifies the required power 

(discharge, regen, and recharge) at various temperatures as a percentage of 30°C power targets.

Performance degradation is allowed at lower temperatures and is linear with temperatures below 30°C.

Table 10. Required battery power capability (as a percent of 30°C value) at various temperatures

Characteristics at EOL (End of Life) Units

High 

Power/Energy 

Ratio Battery

High 

Energy/Power 

Ratio Battery

Unassisted Operating & Charging Temperature Range °C -30 to +52 -30 to +52

30°-52° % 100 100

0° % 50 50

-10° % 30 30

-20° % 15 15

-30° % 10 10

5. Summary 

In support of the U.S. Advanced Battery Consortium, vehicle analysis and battery sizing studies were 

performed to recommend battery requirements. The analysis process included defining vehicle platforms, 

vehicle performance targets, the desired equivalent electric range operating strategy (all-electric or 

blended), and state-of-charge window. Based on the analysis, USABC members recommended two 

categories of batteries, one for a 10-mile EV range (high power/energy ratio) and one for a 40-mile EV 

range (high energy/power ratio). Four sets of requirements were defined: (1) system-level (all-electric 

range, pack cost, calendar life, volume, weight, and energy efficiency); (2) charge-depleting hybrid EV 

(HEV) mode (2-second and 10-second discharge power, 10-second regenerative braking power, available 

energy at constant power, number of deep cycles, maximum recharge rate); (3) charge-sustaining HEV 

mode (available energy for charge-sustaining operation, cold cranking power, number of shallow charge 

sustaining cycles); and (4) battery limits (maximum current, maximum and minimum voltage, operating 

and survival temperatures).

The USABC adopted the requirements proposed by the PHEV Battery Work Group and included them as 

goals in a request for proposals to developers of PHEV batteries. Table 11 is the final version of the 

PHEV battery requirements, targets, and goals as posted on the USABC Web site (please see

http://www.uscar.org/commands/files_download.php?files_id=118). 
13 

Table 11. USABC goals for advanced batteries for plug-in hybrid electric vehicles

Characteristics at EOL (End of Life) High Power/Energy Ratio 

Battery

 High Energy/Power Ratio 

Battery

Reference Equivalent Electric Range miles 10 40

Peak Pulse Discharge Power - 2 Sec / 10 Sec kW 50 / 45 46 / 38

Peak Regen Pulse Power (10 sec) kW 30 25

Available Energy for CD (Charge Depleting) Mode, 10 kW Rate kWh 3.4 11.6

Available Energy for CS (Charge Sustaining) Mode kWh 0.5 0.3

Minimum Round-trip Energy Efficiency (USABC HEV Cycle) % 90 90

Cold cranking power at -30°C, 2 sec - 3 Pulses kW 7 7

CD Life / Discharge Throughput Cycles/MWh 5,000 / 17 5,000 / 58

CS HEV Cycle Life, 50 Wh Profile Cycles 300,000 300,000

Calendar Life, 35°C year 15 15

Maximum System Weight kg 60 120

Maximum System Volume Liter 40 80

Maximum Operating Voltage Vdc 400 400

Minimum Operating Voltage Vdc >0.55 x Vmax >0.55 x Vmax

Maximum Self-discharge Wh/day 50 50

System Recharge Rate at 30°C kW 1.4 (120V/15A) 1.4 (120V/15A)

Unassisted Operating & Charging Temperature Range °C -30 to +52 -30 to +52

Survival Temperature Range °C -46 to +66 -46 to +66

Maximum System Production Price @ 100k units/yr $ $1,700 $3,400

 

6. List of Abbreviations

AER: all-electric range

AT-PZEV: advanced technology, partial zero-emission vehicle

BOL: beginning of life

CD: charge-depleting 

CDH: charge-depleting hybrid (blended) 

CS: charge-sustaining 

E/P: energy to power ratio

EOL: end of life

EV: electric vehicle

HEV: hybrid electric vehicle

P/E: power to energy ratio

PHEV: plug-in hybrid electric vehicle

SOC: state-of-charge 

UDDS: Urban Dynamometer Driving Schedule 

USABC: U.S. Advanced Battery Consortium

ZEV: zero-emission vehicle 
14 

7. References

[1] Markel, T. and Simpson, A., “Cost-Benefit Analysis of Plug-in Hybrid Electric Vehicle Technology,” 22nd 

International Electric Vehicle Symposium, Yokohama, Japan. October 2006. 

[2] U.S. Department of Energy, Plug-in Hybrid Electric Vehicle R&D Plan, February 2007; 

http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/phev_rd_plan_02-28-07.pdf

[3] Rousseau, A., et. al., “Research on PHEV Battery Requirements and Evaluation of Early Prototypes,” 7th

Advanced Automotive Battery Conference, Long Beach, California, May 16-18, 2007. 

[4] Markel, T., et. al., “Plug-In Hybrid Vehicle Analysis,” Milestone Report, NREL/MP-540-40609, National 

Renewable Energy Laboratory, Golden, Colorado, November 2006; 

http://www.nrel.gov/vehiclesandfuels/vsa/pdfs/40609.pdf

[5] Markel, T., “Platform Engineering Applied to Plug-In Hybrid Electric Vehicles,” Society of Automotive 

Engineers World Congress, Detroit, Michigan, April 16-19, 2007. 

[6] Gonder, J., “PHEV ESS Requirements Crossover SUV PSAT Modeling,” communication with FreedomCAR 

Tech Teams, National Renewable Energy Laboratory, Golden, Colorado, March 2007.

[7] FreedomCAR and USABC Energy Storage Goals for Power-Assist HEVs, USABC Web site, November 2002; 

http://www.uscar.org/commands/files_download.php?files_id=83

8. Acknowledgements 

The funding for this work was provided by DOE’s Vehicle Technologies Program, Energy Storage

subprogram. Many contributed to the discussion of the PHEV requirements, including T. Duong (DOE); 

our colleagues from the Energy Storage Tech Team: A. Habib (GM), C. Ashtiani (Chrysler), J. Lee 

(Ford), R. Elder (Chrysler), G. Hendrickson (ANL), N. Pinsky (SCE), J. Belt (INL), and J. Deppe (SRA); 

and our colleagues from the Vehicle System Analysis Tech Team: L. Slezak (DOE), N. Shidore (ANL), 

A. Rousseau (ANL), and J. Gonder (NREL).

9. Authors

Ahmad Pesaran joined National Renewable Energy Laboratory (NREL) in 1983 and has been 

working on various energy systems such as solar cooling, ocean thermal energy conversion, air 

conditioning, desiccant dehumidification/ cooling for buildings and buses, and since 1995, hybrid 

electric vehicle projects. He is currently the project manager for various activities related to energy 

storage, such as battery thermal characterization, battery thermal analysis, electrical management 

and battery and ultracapacitor simulations for vehicle target analysis. Dr. Pesaran holds a Ph.D. in 

mechanical engineering from UCLA. He is a member of the FreedomCAR Electrochemical Energy 

Storage Technical Team and several of its workgroups. 

Tony Markel joined NREL in 1996. He received his M.S. degree in mechanical engineering from 

the University of Colorado in 2005 and a B.S.E degree in mechanical engineering from Oakland 

University in 1995. He was instrumental in the development of the ADVISOR software tool for 

vehicle systems simulation and is skilled at using analysis and optimization tools to address realworld problems. He has supported simulations for setting requirements of batteries for advanced 

vehicles for the USABC. Mr. Markel is a member of the FreedomCAR Vehicle System Analysis 

Technical Team. 
15 

Harshad Tataria is a member of both the United States Advanced Battery Consortium (USABC) 

and the FreedomCAR Energy Storage Technical Team. He is a Staff Project Engineer at General 

Motors Corp, where he is responsible for the development of energy storage systems for HEVs. 

Mr. Tataria has over 32 years of experience in battery development. His experience includes leadacid, NiMH, Li metal primary and secondary, Li-ion batteries, and ultracapacitors. He has obtained 

five patents and published 14 papers in various scientific journals. He is the lead for the USABC 

PHEV Battery Work Group in setting requirements.

David Howell manages Electrochemical Energy Storage Research and Development in the DOE 

Vehicle Technologies program, Washington, DC. For four years he served as the DOE Co-Chair of 

the FreedomCAR Electrochemical Energy Storage Tech Team. Mr. Howell received a Bachelor of 

Science degree in Aerospace Engineering in 1985 from the University of Tennessee at Knoxville 

and subsequently received a commission in the United States Air Force. He has over 22 years of 

R&D project management experience with the USAF Materials Laboratory at Wright Patterson 

AFB, Oak Ridge National Laboratory, and the U.S. Department of Energy. 
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14. ABSTRACT (Maximum 200 Words)

Plug-in hybrid electric vehicles (PHEVs) could displace a significant amount of petroleum in the next 10 to 20 years. 

The main barriers to commercializing PHEVs are the cost, safety, and life of batteries. Therefore, the U.S. 

Department of Energy and auto companies embarked on a program to develop batteries for PHEVs. Defining battery 

targets or requirements to benchmark progress was essential. The DOE-industry U.S. Advanced Battery Consortium

(USABC) sponsored analysis and battery sizing studies to recommend battery requirements. This included defining 

vehicle platforms, performance targets, an equivalent electric range operating strategy (all electric or blended), and 

the state-of-charge window. The studies recommended two battery categories: one for a 10-mile equivalent electric 

vehicle (EV) range (high power/energy ratio) and one for a 40-mile EV range (high energy/power ratio). This paper 

presents the assumptions, analysis, discussions, and resulting requirements adopted by the USABC. 

15. SUBJECT TERMS

plug-in hybrid electric vehicles; hybrid electric vehicles; PHEV; battery, EV range, charge-depleting

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