Storage

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All lead-acid batteries will self-discharge when allowed to stand on open circuit. This self-discharge is due to "Local Action" caused by dissimilar metals (positive vs. negative plates) used within the cell's construction. The result of the self-discharge is loss of cell open circuit voltage, consequently loss of capacity. If allowed to progress beyond the normal limits, excessive plate sulfation may occur causingpermanent loss of capacity and premature battery failure.

The PRC Series batteries have been designed to minimize the effects with the use of the purest plate materials available. This has resulted in a reduction of the self-discharge rate to approximately one-fifth of a conventional lead acid battery. The rate of self-discharge will also be dependent upon the battery's storage temperature. Lower storage temperatures will reduce the self-discharge rate, higher temperatures will increase the rate. A cool, dry area is the recommended environment in which batteries should be stored. They should also be placed away from any heat sources including heaters, steam pipes, equipment or in direct sunlight. The table below represents the maximum allowable storage time at various battery storage temperatures.

Storage parameters

Battery open circuit voltage:

A useful tool in determining the battery's state of charge while in storage is the open circuit voltage (O.C.V.). The O.C.V. is a relative measure of the electrolyte concentration (specific gravity) contained within the battery. The electrolyte specific gravity is a direct measure of the battery's state of charge and can be used to determine the percentage of battery capacity remaining at any given point. This relationship is exhibited on the "Battery Open Circuit Voltage vs. Percent Remaining Capacity" curve (DWG# BSD- OCV PRC). From this curve it can be seen that a battery voltage of 1.98 V.P.C. (11.88 for 12 volts, 5.94 for 6 volts) or less will have zero percent capacity remaining. In order to prevent any possible permanent plate damage from occurring due to self-discharge, it isrecommended that when any battery in storage has an O.C.V. corresponding to the 50% capacity level (12.40 for 12 volts, 6.20 for 6 volts), it should be promptly recharged.

Using these parameters, one can take advantage of the longest possible storage durations without subjecting the battery to any potential harm caused by the delirious effects of prolonged self- discharge. The open circuit voltage (O.C.V.) can also be useful in approximating the remaining storage time available before the batteries reach the minimum O.C.V. (12.40V / 12V or 6.20V / 6V) before recharge. A curve has been provided to show the relationship of "Battery O.C.V. vs. Percent Storage Time Remaining" (DWG. # BSD- OCVPST). To use this curve take the O.C.V. of the battery and locate the point on the curve which intersects with the percent remaining storage time. This percentage is then multiplied by the storage time and temperature parameters given earlier to calculate the approximate storage time remaining before required recharge. It should be noted that the battery's O.C.V has some limitations on it's accuracy. The percent capacity remaining is within -10% or +10% if the battery has been on charge or discharge within the last 24 hours. After a battery has remained on open circuit for a minimum of 72 hours the accuracy increases to -2.5% or +2.5%

Notes

The battery O.C.V. can also be used in approximating the state of charge after a discharge using the same parameters as described above. However, it should be noted that this does not apply for the percentage of remaining storage time curve as all batteries should be recharged immediately after a discharge. All PRC Series batteries should be recharged using a constant voltage of 2.25 - 2.37 V.P.C., at 77°F, for a minimum of 24 hours or until the float current stabilizes for 3 consecutive hourly readings. Battery carton date coding All PRC Series battery cartons are date coded with a recommended recharge data. The date code (month / year) has been calculated for "normal " storage tempe- rature conditions (66°F - 90°F) and dated 6 months from the battery's last full charge. The battery's O.C.V. should continue to be checked at frequencies described earlier to give a true indication of when a battery will require a recharge. Battery terminal date coding All PRC Series batteries are date coded on the positive and negative terminal flags. Coding consists of date of manufacture, and battery type designation and follows the procedure described below. Battery date coding and type designation:

  1. 1- Type of battery, stamped by external terminal burner on positive terminal flag.
  2. 2- Number stamp indicating month out of Formation Department stamped by high-rate personnel on negative terminal flag.
  3. 3- Number indicating year out of Formation Department is to be stamped by high-rate personnel on negative terminal flag, directly under stamp indicating month of formation.

Refer to Dwg. # BID-DCI, top view, for location of date codes.

Notes

PRC-636 batteries will be hot stamped, on side of cover where positive external terminal tab is located. Refer to Dwg. # BID-DC2 PRC-1225 batteries will be hot stamped on side of cover where positive external terminal is located. Refer to Dwg. # PRC-1225X-FAD Battery "Shut down and storage": Due to the natural self-discharge of the PRC Series batteries, many of the storage parameters discussed earlier would apply when "shutting down" and storing a battery system. As before, the battery's O.C.V. is a useful tool in determining when a recharge would be required. All batteries placed in storage should be fully charged before shutting down and disconnecting from the system.

The batteries may also need to be relocated if the environment is not suitable for storage (refer to storage parameters). When shutting down a battery system which has been in use, some additional considerations will need to be made. First, and foremost, the batteries must be fully charged before the equipment is shut-down. Second, the battery must be disconnected (via disconnected, breaker, etc.) completely from the equipment circuitry. One must insure that all possible loads are also disconnected so that the batteries are not unknowingly discharging during the shut-down period. Examples of other small loads may be shunted devices or other small resistive loads tied into the circuit. As an additional safety measure one of the battery fuses or intercell connections can be removed.

Caution: Be sure battery system is disconnected from circuit before removal of any intercell connectors.

Finally, record the date when the system was shut down and include this with the regularly scheduled maintenance records for future use. It may also be advisable to place a recharge date directly on the batteries as a additional visual aid to indicate when a recharge would be required.