Abstract:
The invention is an automated single point battery watering system which has a battery watering control system comprising a fluid reservoir, a fluid delivery header for delivering fluid from the reservoir to the cells of at least one battery, a flow controller in communication with the fluid delivery header for controlling the flow of fluid from the reservoir through the header, and a monitoring system for monitoring the battery charge state and for timing the activation of the flow controller for adjusting the flow relative to the state of charge so that over watering does not occur. Also included is a fluid restrictor associated with the fluid delivery system to limit gas flow into the fluid delivery header.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority in U.S. Provisional patent application No. 60/629,183 filed Nov. 17, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to a filling system for adding replenishment water to one or more secondary batteries, each typically comprising multiple cells, and more particularly, to an automated battery watering control system that monitors and senses whether a battery is in condition for watering.  
         [0003]     Secondary battery cells, for example, lead-acid battery cells, have a liquid or flowable electrolyte that requires periodic replenishment of water lost from the electrolyte through electrolysis and evaporation.  
         [0004]     The process of adding water can be simple when the number of batteries and the number of battery cells is small, and there is available manpower. However, it is increasingly common for some facilities to have tens or even hundreds of batteries in use. The number of individual cells that must be periodically filled is thus quite large. To meet this need, single point battery watering equipment is available which can be set up as a watering station where multiple batteries can be located and filled at the same time. Such equipment usually has a large reservoir and means for dispensing fluid to the multiple battery cells.  
         [0005]     In facilities having a large number of batteries, it is common for individual batteries to be in different states of discharge at any given time, due to differences in usage, age or other factors. Thus, some batteries will require recharging before others, which makes scheduling recharges somewhat difficult.  
         [0006]     Another problem is that batteries, such as lead-acid batteries, cannot be watered when they are at a low state of charge since the electrolyte expands on charging. If filled during a low state of charge, subsequent charging can cause the electrolyte to attain an excessively high level, with electrolyte overflowing the cells. As the electrolyte is typically sulfuric acid, such overflows must be minimized to avoid damage to adjacent structures.  
         [0007]     Consequently, the logistics of providing water to many batteries that are in a variety of states of charge throughout the working day can be difficult, even with use of single point battery watering equipment.  
         [0008]     These problems may be reduced, though not eliminated, by using a watering controller which operates in conjunction with the battery charger. Such a controller provides water to the battery automatically when the battery state of charge is sufficiently high.  
         [0009]     Although intended to free battery operators from being in attendance during the battery watering operation, in practice, such a control strategy was often found to provide the batteries with more water than was needed. In addition, the associated watering systems became so complicated that an operator was still required to monitor watering and to occasionally intervene to avoid overwatering or overflows.  
         [0010]     For example, if a battery had not been used between watering cycles, and was then connected to the system, the battery would receive water since it was still in a charged state, even though no water was in fact needed, resulting in double watering. This was because the water addition system was activated at about 80% state of charge, apparently chosen to take advantage of gassing that occurs when charging at that state to mix the water with the electrolyte. Unfortunately, this simply put more water into a cell having an already high level of electrolyte, with further expansion during charging resulting in an electrolyte overflow.  
         [0011]     Another problem can occur should the water reservoir run dry, which could also leave the water distribution tubing mounted atop the battery cells dry as well, thereby allowing the tubing to act as a conduit for gas evolving in the battery, which could lead to hydrogen gas accumulation in the tubing and reservoir.  
         [0012]     While watering controllers provide an opportunity to charge and add water to batteries overnight and over weekends, completely unattended, as described above, such inattention can lead to electrolyte spillage and/or gas filled tubing necessitating corrective action and cleanup. Consequently, most users of these systems have not been willing to risk such occurrences, and require an operator to be present to monitor the filling process.  
       SUMMARY OF THE INVENTION  
       [0013]     It is an object of the present invention to provide a battery watering control system which avoids the above referenced problems.  
         [0014]     It is a further object of the present invention to provide a battery watering control system which can truly be run successfully with little to no operator attention.  
         [0015]     It is yet another object of the present invention to provide a battery watering control system which substantially avoids overwatering.  
         [0016]     It is another object of the present invention to provide a battery watering control system that minimizes the possibility for battery gas to enter the watering system.  
         [0017]     These and other objects of the present invention are achieved by a battery watering control system comprising a fluid reservoir, means for delivering fluid from the reservoir to at least one battery, flow control means in communication with the conduit means for controlling the flow of fluid from the reservoir through the delivery means, and means for monitoring the battery charge state and for timing the activation of the flow control means relative to the state of charge such that overwatering does not occur. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a view of the battery watering control system of the present invention.  
         [0019]      FIG. 2  is a cross-sectional view of the portion of the delivery system located in a battery watering opening.  
         [0020]      FIG. 3  is a view showing the battery receiving water from the watering control system.  
         [0021]      FIG. 4  is a view showing the battery watering system by-passing a filled battery cell.  
         [0022]      FIG. 5  is a view showing the battery watering system after completion of the watering operation.  
         [0023]      FIG. 6  is a schematic view of a control diagram usable with the present invention.  
         [0024]      FIG. 7  is a graph showing percent electrolyte expansion relative to the volts per cell. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]      FIG. 1  is a schematic representation of the control monitored single point battery watering system  10  of the present invention. A battery  12  has, by way of example, six cells  12   a - f , the battery  12  fitted with a plurality of water flow-control caps,  14 , interconnected by a header  13 , as will be described in more detail below. The number of caps will correspond to the number of cells to be filled, and these can be arranged to fill multiple batteries at the same time, tailored to the needs of the facility where the system is located. Six cells is chosen merely for convenience and to simplify the discussion and drawings, as would be understood by one skilled in the art, as the system can easily be scaled up to supply battery water to virtually any number of cells.  
         [0026]     The watering system  10  has a water source or reservoir  16  that contains a fluid for delivery to the battery cells. It should be understood that the fluid may be water alone or include suitable additives, and the terms “water” or “watering”, are not limited to solely water as the fluid to be administered.  
         [0027]     A battery charger  18  is connected to battery terminals  19   a  and  19   b  for recharging the battery  12 . A watering controller  20  controls the delivery of the fluid to the battery  12 . Preferably the fluid is delivered following charging of the battery to a selected level of electrical charge, as will also be described further below.  
         [0028]     The watering system  10  has a flow control valve  24  which is preferably an electrically operated normally closed solenoid valve. In this embodiment, a fluid coupling  26 , which may be a quick connect coupling, threaded coupling, etc., is used to connect the valve  24  to the header  13  feeding the flow control caps  14 . An electrical coupling  28  may be used to connect the charger  18  to the battery terminals. For example, any male/female electrical connector suitable for use with the voltages/amps involved can be used. Such connectors allow the system to be quickly associated with different batteries.  
         [0029]     The flow through the water flow-control caps  14  is illustrated in  FIGS. 2, 3 ,  4  and  5 , as will be described further below. These are arranged to provide self-priming water barriers which form an important part of the control monitored single point battery watering system  10  of the invention.  
         [0030]     The battery  12 , the water reservoir  16 , the battery charger  18 , the solenoid valve  24  as well as the two couplings  26  and  28  are all of a type well known to persons skilled in the art and therefore require only a brief explanation here. However, the watering controller  20  contains unique operational aspects that in conjunction with the water flow-control caps  14  provide a system that can truly be run, reliably, unattended, thereby facilitating battery charging and watering in off-hours or on off days, reducing operating costs while increasing efficiency. Further, by limiting overflows and electrolyte spills, and reliably providing the proper amount of water to the batteries over the life of the batteries, that life itself may be extended. It is well know that a proper battery watering schedule can prolong battery life and the system of the invention makes this much more likely to occur.  
         [0031]     The battery  12  has six cells, as shown in  FIG. 1 , each cell being fitted with an individual water flow-control cap annotated in a sequence as  30 ,  32 ,  34 ,  36 ,  38  and  40 . The water flow-control caps are connected in series by the fluid header  13 , though they may also be connected in parallel or in a series-parallel combination. In this embodiment, the coupling  26  is connected to the cap  30  by a length of tubing  46 , the cap  30  connected to the cap  32  by a length of tubing  48 , the cap  32  to the cap  34  by another length of tubing  50 , etc, sequentially to the end cap  40 , beyond which the fluid header is closed.  
         [0032]     The tubing  46  has a length sufficient to provide ease in the connection and disconnection of the header  13  to the coupling  26 . The battery  12  is connected to the electrical coupling  28  by a pair of cables  60  and  62 , or by a single cable with two conductors therein, the cables being movable to another battery after the battery  12  has been charged and replenished.  
         [0033]     The water reservoir  16  is preferably positioned above the battery  12  to provide gravity flow to the battery  12 , though gravity feed is not the only way of supplying the fluid to the header, such as by use of a pump, though gravity feed has the advantage of reliability and low cost.  
         [0034]     A fluid conduit  42  is provided between the water reservoir  16  and the first of the water flow-control caps  30 . The solenoid valve  24  and the fluid coupling  26  are integrated with the conduit, to complete the water supply circuit.  
         [0035]     The battery charger  18  has a pair of terminals  52  and  54  connected to cables  56  and  58  which conduct the charger output current to the battery  12  via the electrical coupling  28 , with a polarity and magnitude suited to the battery  12 .  
         [0036]     The fluid coupling  26  and the electrical coupling  28  connect and disconnect independently. They may, however, be integrated into a single assembly for ease in attachment to the battery. Preferably, the open ends of the fluid conduits exposed when the fluid coupling  26  is disconnected have self-closing barriers, which close when the fluid coupling  26  is disconnected, and which open when it is connected. These barriers may be fitted to one or both sides of the fluid coupling  26 .  
         [0037]     The electrolyte level of an industrial motive power flooded-type lead-acid battery rises significantly towards the end of charge, and an addition of replenishment water to a discharged battery that appears to be a correct level can result in the level rising to a point of overflowing when the battery is subsequently charged.  
         [0038]     The battery control scheme which utilizes a monitoring controller is next described. As discussed above, to avoid any risk of overflowing, and of corrosive acid spills, the battery should only be replenished when the electrolyte has attained a maximum level, which occurs at the end of the charging process.  
         [0039]     The voltage of a lead-acid battery on charge rises very slowly from a fully discharged state, to about 80 percent. Approaching 100 percent state-of-charge, the battery voltage can increase from 2.35 volts per cell, to 2.6 volts, and even 2.8 volts per cell. A voltage in excess of 2.35 volts per cell causes the battery to gas, and an accumulation of gas bubbles can occur below the level of the electrolyte which raises the electrolyte level significantly. Other factors that contribute to raising the electrolyte level are chemical—there is more acid in a charged battery- and thermal—the process of charging warms and expands the electrolyte.  
         [0040]     Upon cessation of charging the battery voltage declines fairly rapidly from its on-charge potential to its rest potential. The change is most pronounced when the battery is at a full state-of-charge.  
         [0041]     The watering controller  20  has means to monitor the voltage of the battery  12  via a pair of sensing leads  64  and  66 , connected at the battery charger terminals  52  and  54 , which carry the voltage of the battery  12  during the charging process. In one embodiment of the invention, the battery charger  18  and the watering controller  20  can be physically and/or functionally combined in a unitary housing.  
         [0042]     One way to integrate the detection of the cessation of charging with the watering controller  20  is to detect a substantial voltage declination across the pair of terminals  52  and  54 , due to a power rectification process within the battery charger  18 , and to issue a signal to the flow control valve to open and supply fluid only when that point is reached. Preferably, the monitored voltage is processed by an averaging circuit before being utilized by the watering controller  20 .  
         [0043]     The watering controller  20  needs to open the valve only for a period of time sufficient to replenish the battery  12 . For example, in the case of a medium sized forklift battery, as used in a warehouse, the requirement is likely to be for about 200 milliliters of replenishment water per cell per working week. Since the battery is likely to be charged daily, an 18 or 24 cell battery will need up to a liter of water per daily cycle. Consequently, the appropriate watering time should be set in the watering controller.  
         [0044]     Another factor to consider in the watering time is that it is a characteristic of all secondary batteries that they require more energy to be put in than was previously taken out. Consequently, battery chargers are arranged to provide a degree of overcharging, which can vary according to the type of charging equipment, depth of discharge of the battery, temperature and many other factors. Consequently, the replenishment requirement of a battery may vary quite significantly, requiring an adjustment of the determined opening time of the valve  26 .  
         [0045]     One problem that can occur is that power interruptions and brownouts can provide false end-of-charge signals. Also, disconnection of a battery prior to attaining a 100 percent state-of-charge can result in insufficient watering. Furthermore, attempting to charge a battery, already at, or near 100 percent state-of-charge can provide excessive watering. Moreover, certain types of battery chargers apply a succession of current pulses following termination of charging, causing the battery voltage to rise and fall significantly. This succession of pulses can result in repeated, inadvertent watering.  
         [0046]     The watering controller  20  of the present invention is capable of obviating these disadvantages, by using a monitoring system that can detect these “false” watering conditions, and thereby prevent water flow. While the watering controller  20  can be constructed from discrete electronic functional units, for example, logic gates, counters, etc. it is preferred to use a microprocessor architecture to incorporate the monitoring system of the invention, and it is possible to implement this by way of a software and/or hardware solution. For example, some or all of the functions can be provided on a programmable chip, and the invention is not limited to any one particular means for providing the monitoring system of the invention.  
         [0047]      FIG. 6  depicts a logic diagram that may be used in a typical embodiment of the invention. Generally, this begins after the battery is attached to the charger, and the filling apparatus has been properly located for filling the individual cells. After this occurs, the controller is powered up. The sequence commences with pressing a start button or by receiving a command to begin. After Start, the watering controller  20  proceeds to Read Voltage on Battery  12 . If the battery charger  18  is not immediately switched on, the Voltage Rise? will not occur, and register No, returning the system to Read Voltage on Battery. When the charger  18  is switched on, there will be a rise in voltage, and so the query response to Voltage Rise? will switch to Yes, and the controller will proceed to Start Timer.  
         [0048]     The watering controller  20  continues to monitors the rise in voltage due to the battery  20  being charged by the charger  18  over a specified time period, for example, within 20 minutes of commencement of charging. This provides a damping period to avoid improper watering. If the Is Voltage Over 2.4 Vpc within 20 min? query is answered Yes, no watering is undertaken. This is because if the battery  12  when connected is already fully charged, the rise in voltage per cell will exceed 2.4 V. within 20 minutes of charge initiation. In such a case, no watering should be undertaken. If the battery is low on charge, i.e. been discharged, but not over discharged, its voltage per cell should lie somewhere between 2.1 and 2.3 volts, in accordance with the volts per cell curve in  FIG. 7 , depending on the number of charging hours remaining to bring it up to a full state of charge. Note that the information presented in  FIG. 7  represents a taper charge at a temperature of 15° C.  
         [0049]     If the battery  12  has been over discharged, any addition of water will further dilute the electrolyte and make it more difficult for the battery to accept charge. However, such a battery will also display a rise in voltage that exceeds 2.4 V per cell within 20 minutes of charge initiation, and so the watering controller  20  “sees” the battery  12  as already charged, and will not initiate the watering sequence.  
         [0050]     If there is a voltage rise above 2.4 v per cell within 20 minutes, the controller  20  receives a Yes response, and by-passes the watering sequence and terminates by the Go to Watering Complete and End steps. Note that this condition also addresses the situation where the battery may have become prematurely unplugged. When this happens, the battery  18  may be “offered” another opportunity to accept water during the course of the next charging operation. Since the system can determine whether a battery has already been charged, there is no harm in re-checking the battery status periodically to determine if further charging is appropriate.  
         [0051]     If the voltage per cell remained under 2.4 for 20 minutes, the controller  20  proceeds via No to the watering arming phase. This has two steps. First, it monitors the voltage to see if it reaches 2.5 V per cell, and then it waits for the voltage to fall. This is what occurs when the battery is at about 80% of charge. Then when the voltage per cell falls below a threshold level, for example, 2.3 V for about 10 minutes, this indicates that the charging is complete, and so watering can safely begin. Thus, the controller monitors voltage and when the Voltage at 2.5 Vpc. Arming phase+wait for Vcp to Fall is achieved and the Voltage falls below 2.3 Vpc for +10 mins? answer is Yes, then the controller issues a signal for watering to begin by opening the flow control valve.  
         [0052]     Thus the end of charge is recognized by the controller  20  when the volts per cell exceeds 2.5 V and then begins to fall. If the volts per cell does not go over 2.5 V and yet the volts per cell begins to fall, the controller  20  perceives this as a possible power outage or brownout, and watering will not begin. This allows the charger  18  more time to complete its task.  
         [0053]     When the voltage per cell falls after attaining 2.5 V, the control sequence will continue to circulate via No and Voltage at 2.5 Vpc. Arming phase+wait for Vpc to Fall and Voltage Falls below 2.3 Vpc for +10 mins? Eventually the voltage per cell does fall below 2.3 V for 10 minutes and the sequence switches to Open Solenoid Valve for Preset Time via Yes. This preset time period corresponds to the timing interval that the flow control valve is open, such as when the electrically operated normally closed solenoid valve is energized, and a portion of the water  22  is permitted to flow from the reservoir  16  to the cells of the battery  12 .  
         [0054]     If the charger  18  should provide a form of end-of-charge pulsing, causing the potential of the battery to vary up and down, each successive rise in potential causes the Voltage falls below 2.3 Vpc for +10 mins? sequence to default to No and therefore watering will not be permitted until at least 10 minutes following the last pulse.  
         [0055]     This aspect has been shown occurring once, as a voltage spike or charging pulse p 1  on the volts per cell curve during the interval t 2  to t 3  in  FIG. 7 . While only one pulse has been shown in  FIG. 7 , it is usual for pulsing to be repeated. These repeats have not been shown for the sake of clarity of the illustration.  
         [0056]      FIG. 7  also shows an electrolyte expansion curve expressing the percentage between minimum and maximum level of the electrolyte due to the charging process, a difference which can exceed 50 millimeters in respect of the tallest industrial cells currently in use.  
         [0057]     While there is a widely held belief that watering after charge is best avoided since it can lead to stratification of the water above the electrolyte, this belief only applied from the days when it was common for batteries to be watered infrequently and therefore the sheer volume of water being added naturally took a long time to mix with the rest of the electrolyte. This does not apply to watering after every successive charge since the amount of water then being added will be so small as to mix practically instantaneously. Nevertheless, the typical control strategy in automatic watering systems in use today is still to water the batteries before the end of charge, in line with the proposed embodiment of U.S. Pat. No. 4,359,071.  
         [0058]     However, the inventor has determined that this is not the optimum control strategy, as watering the tallest cells before the end of charge, with reference to the expansion curve shown in  FIG. 7 , if done 1½ to 2 hours before charge completion, would likely provide about 30 millimeters over and above the normal electrolyte level and this could push some of the electrolyte out of the cells upon attainment of full state of charge.  
         [0059]     The present invention takes advantage of the falling level of the electrolyte, as illustrated in  FIG. 7 , upon cessation of charging. According to the invention, the timing interval t 3  to t 4  corresponds to the duration the water  22  is applied to the battery  12 , the timing interval t 1  to t 2  corresponds to the duration of charging the battery  12  by the charger  18 , and the timing interval t 2  to t 3  corresponds to the delay after charge completion before commencement of watering.  
         [0060]     Overwatering due to attempted charging of an already fully charged or nearly fully charged battery is prevented by the control sequence Voltage Rise?—Yes—Start Time—Is Voltage Over 2.4 Vpc within 20 Min?—Yes as illustrated in  FIG. 6 . With reference to  FIG. 7  the sequence Voltage Rise? go to Yes corresponds to t 1 —the commencement of charging and the sequence Start Timer—Is Voltage Over 2.4 Vpc within 20 min? go to Yes corresponds to a routine that detects the battery  12  as being already fully charged or nearly fully charged at the time of its connection to the charger  18  corresponding to Start-Plug Battery Into Charger. Detection of an already charged condition of the battery  12  is made possible through a characteristic of the type of battery in use, which causes the voltage of the cells to rise very quickly upon application of a suitable charging current, occurring, for example, within a 20 minute time period from start of charging, as permitted by Is Voltage Over 2.4 Vpc within 20 mins? More specifically, it corresponds to a period of detection from t 1  to t 1 +20 minutes, (or any other suitable timing interval).  
         [0061]     A problem facing the battery maintenance industry has been a growing preference for more compact battery construction. This may be achieved by reducing the available headroom or space above the electrolyte and below the cell lids. Of course, this restricts the volume available for electrolyte expansion. Thus, watering before end of charge poses an increased risk of overfilling when using the prior automatic watering systems, requiring more frequent operator oversight when such compact batteries are used.  
         [0062]     The change in control strategy of the present invention, watering after t 2 , is a significant step towards achieving automated watering, even of these compact batteries, without operator intervention.  
         [0063]     Another improvement is the use of a control strategy that detect if a battery already is in a high state of charge, by monitoring a comparatively rapid voltage rise soon after the battery has been put on charge, during the period of t 1  to t 1  plus a suitable timing interval.  
         [0064]     Furthermore, the inventive control system eliminates power outages and brownouts as false signals that watering is required, allowing watering to be delayed.  
         [0065]     The inventive control system also uses voltage monitoring to detect an end of charge, which provides an effective battery watering signal, typically interval t 3  to t 4 , following the last of n charging periods, of which at least one period constitutes the bulk of the charge.  
         [0066]     In conjunction with the novel control system, there is used a preferred cell filling system which improves reliability for the distribution system, thereby rendering it more likely that the system can run unattended. This relates to the use of a water sealing or gas flow obstruction arrangement integrated with the water flow-control caps located on the battery  12 .  
         [0067]     Generally, comparatively narrow bore tube portions are used on the inlet and outlet sides of each water flow control cap, which are of such a diameter that a quantity of fluid is retained therein by capillary action. This has not been found to be an impediment to water flow and feed to the cells, but when the flow stops, instead of draining out, water is retained within the tubing portions which surprisingly provides an effective barrier to a flow of gas effluent from the battery cells into the water feed or fluid conduits associated with the water flow-control caps. In such a case, there is significantly less risk from unattended operation, for example, if the reservoir runs dry, as the fluid retained in the tube sections keeps any gas effluent sealed in the battery. These capillary sections provide an effective contribution towards safety and reliability, and in conjunction with the control system of the invention, in particular, towards achieving a truly unattended battery watering operation.  
         [0068]      FIG. 2  shows a schematic section of the water flow-control cap  30  located on an associated battery cell  72 , which for clarity only, are shown temporarily without any water and without any electrolyte. The cap  30  is generally similar to a battery filler unit described in U.S. Pat. No. 4,544,004 to Fitter et al, the disclosure of which is incorporated herein by reference in its entirety.  
         [0069]     The cap  30  is connected to the tubing  46  and  48  by means of a tee  76 , communicating with an antechamber-like fluid conduit comprising a downwardly projecting tube  78  and connectable to a valve arrangement or valve seat  80 . A concentric valve  82  comprising an outer sleeve and an inner cone, connected by a support bridge, is located within a float  84  which is made of a closed cell foamed plastic to provide buoyancy in water. The valve  82  and the float  84  are located within a cup-like enclosure with lid  86 , and the float  84  is shown resting on a plate  88  having a downwardly projecting wall  88   a  which forms a water trap  90  in conjunction with concentric base walls  86   a  of the cup-like enclosure  86 . The inner base wall  88   a  of the cup-like enclosure  86  extends downwardly to form a vertical level sensing tube  94  having a flanged orifice or aperture  92  at its top, and an open mouth  96  at its bottom. The cap  30  includes a breather tube  98  which permits passage of any effluent gases emanating from the region of a set of electrodes  100  to the exterior of the cap  30 .  
         [0070]     In operation, water emerging from the downwardly projecting tube  78  will continue downwards, past the cone of the valve  82 , and hence under the float  84 , and if sufficient water accumulates, will provide an upthrust by means of flotation so as to drive the cone of the valve  82  towards closing of the valve seat  80 . The plate  88  is fixed in position, and will allow a portion of the incoming water to flow immediately via the water trap  90  and the aperture  92 , down the center of the level sensing tube  94 , into the cell  72  below.  
         [0071]     This is more fully illustrated in  FIG. 3 , which shows the battery cell  72  containing an electrolyte  102  receiving a stream of water  104  from the cap  30 , for example, when the watering controller  20  has energized the solenoid  26  and water  22  is permitted to flow via the fluid conduit to fill the lengths of tubing  46  and  48 , the tee  76  and the downwardly projecting tube  78  with a volume of water  22 A.  
         [0072]     The flow of water  104  out of the aperture  92  drains a portion of the water  22 A that might otherwise accumulate in the cup-like enclosure  86 , and thus deprives the float  84  of a full extent of buoyancy—at least until the water  104  ceases to flow. Consequently, the float takes up a position that results in narrowing, by closing the valve  82  against the valve seat  80 .  
         [0073]     In  FIG. 4 , the electrolyte  102  has risen to a level  108  which is sufficient to increase air pressure inside the level sensing tube  94  to cause the water flow to be arrested and to form a substantially static drop  106  in its place. The float  84  quickly rises to close the valve  82  against the valve seat  80 .  
         [0074]     The various tubes and flow paths, including the tubing  46  and  48 , the tee  76  and the downwardly projecting tube  78 , contain residual water  22 A, as shown in  FIG. 4  and this can provide a barrier against gas entering the watering system  10 .  
         [0075]      FIG. 5  shows the water flow-control cap  30  located on a cell  72 , corresponding to the cap and associated cell in  FIG. 1 . The next-in-line cap  32  is located on an adjacent cell  74 , as shown in  FIG. 1 .  
         [0076]     The battery  12  in  FIG. 5  has been in use, and consequently the electrolyte  102  of the cell  72  has fallen to a level  112 . Residual water  114  remains in the water trap  90 , and an almost negligible amount of water  22 B remains inside the lengths of tubing  46  and  48  and the tee  76 . Although the valve  82  has withdrawn from the valve seat  80 , due to the float having come to rest on the plate  88 , the downwardly projecting tube  78  continues to accommodate a plug of water  116  within it.  
         [0077]     Upon investigation, this surprising retention of liquid within a vertical tube, though subject to gravity, was found to be due to capillary action, and also found to occur in the caps  32 ,  34 ,  36 ,  38  and  40  of  FIG. 1 . So strong was this retention that removal of a watering cap from the cell could easily be effected without significantly disturbing the water plug  116 . Subsequent rotation of the cap  30  in various directions so as to move the axis of the tube  78  from vertical to horizontal, and back repeatedly, as well as to rotate the axis of the tube  78 , appeared to have no detrimental effect on the persistence of the water plug  116  within the tube  78 .  
         [0078]     It was found that the inner bore diameter of the downwardly projecting tube  78  played an important role in providing retention of the water plug  116 , the narrow bore providing good retention, while a wide bore provided poor retention. As a general guide, bore diameter of up to 4 or 5 millimeters appeared to give good retention, while larger bores seemed to lose retention more quickly with increase above these diameters.  
         [0079]     Experimentation revealed a variety of tube geometries suitable for use in applications corresponding to the tube  78 . For example, a tube having different diameters along its length, differing cross sectional shapes, bends, junctions, as well as multiple flow paths, including a tube with a porous material filling so as to provide multiple capillary passages have been found suitable. Water retention remained satisfactory in all orientations.  
         [0080]     In an arrangement including consecutive tube section having different diameters, it was found that the narrower bore section contributed to the persistence of the water plug  116 .  
         [0081]     While the wetability of the inner bore surface might appear a significant factor in the plug retention, the use of Teflon (PTFE-polytetrafluoroethylene)—a polymer know for its exceptional non-wetting characteristics—provided only a marginally less effective plug, somewhat akin to the use of a wider inner bore diameter.  
         [0082]     By way of example, a 30 mm length of PVC tubing, having an inner bore diameter of 3 mm retained a 13 mm length plug in all orientations after being filled with water, a 30 mm length of ABS tubing retained 9 mm, while a similar length of PTFE retained a length of 6 mm.  
         [0083]     It is normal for battery cells to emit gas from the region of the electrodes  100  almost continuously, and especially briskly upon attaining a full state of charge. This causes sufficient agitation of the electrolyte  102  to produce an acid mist or spray, a portion of which has been found to project via the breather tube  98  into the cup-like enclosure  86 , along a path indicated by a series of dashed arrows  120 .  
         [0084]     A smaller portion of the acid mist or spray has been found to enter the downwardly projecting tube  78 , thereby to sustain, and even to augment the plug of water  116  within the tube  78 .  
         [0085]     A consequence of the presence of the water plug  116  inside the downwardly projecting tube  78  is to provide an obstruction to passage of gas, from within the cup-like enclosure  86  to the tee  76 , and hence into the lengths of tubing  46  and  48 , and vice versa. A need to rely on a gas flow preventor to accomplish this function is thereby obviated.  
         [0086]     Accordingly, any gas emitted from the region of the electrodes  100  is more likely to follow a path via the breather tube  98 , out of the cup-like enclosure  86  and hence to the exterior of the cell  72 , through a vent slot  118 , generally as indicated by a series of plain arrows  122 .  
         [0087]     While capable of providing an obstruction within the downwardly projecting tube  78 , the water plug does not provide an absolute barrier in the sense of what an impermeable solid object might be expected to provide. It is possible that effects including diffusion and mechanical vibration could assist almost imperceptible quantities of gas originating from within the cell  72 , to traverse the obstacle provided by the water plug  116 . However, it is likely easier for such quantities to escape from the enclosure provided by the fluid conduit, thereby negating an ongoing buildup.  
         [0088]     While the need to rely on a purpose-made gas flow preventor has evidently been obviated, it is feasible by way of supplement to include any variety of devices having an equivalent function.  
         [0089]     An electrically initiated single point battery watering system for providing a controlled flow of replenishment water into a battery, preferably including a capillary duct feed system for conveying water to each cell of the battery, has been described.  
         [0090]     While particular embodiments of this invention have been described, it will be understood, of course, that the invention is not limited thereto since many obvious modifications can be made, and it is intended to include within this invention any such modifications as will fall within the spirit and scope of the appended claims.