Does a battery self-discharge? Yes!

All automotive wet batteries will slowly loose charge when not in service. This is known as self-discharge.

Standard maintenance free batteries containing certain grid alloys, self-discharge at a lower rate than deep cycle batteries. The rate of self-discharge increases with increasing temperature; this is true for both maintenance free and deep cycle batteries.

Allowing batteries to stand for an extended period of time without recharging them, will result in reduced performance and service life. To preserve optimum battery performance and life, recharge batteries in storage when the open circuit voltage drops to 12.4 volts.

To make up for self-discharge while in stock, a boosting charge should be given to batteries whenever they fall .040 points in specific gravity, corrected to 80°F (26.7°C). The boosting charge should be administered regardless if the batteries are to remain in stock or are being prepared for sale. This boost charge will normally be required after about 15-40 weeks of storage at 30°F (-1.12°C). The specific gravity drop will occur faster at elevated temperatures and slower at reduced temperatures. Observe the level of electrolyte before putting a battery on charge, and if necessary, add water to the cells to bring them to proper level.

A charge rate of 3% of the Reserve Capacity rate should be used to charge the battery. The charging should continue until the specific gravity of the electrolyte, corrected to 80°F (26.7°C), is constant over three successive readings taken at one hour intervals.

Some batteries may be sealed in a way that does not allow the specific gravity to be checked. The charging rate for these batteries is also 3% of the Reserve Capacity rate. The length of charge should be one half of the Slow Charge time on the Battery Charging Guide. For example, a battery rated at 100 minutes of Reserve Capacity and reading 12.4 volts should be charged at 3 amps for 10 hours.

Storing batteries for long periods of time without recharging them may accelerate grid corrosion and form boundary layers of non-conductive material between the grid wires and the active materials. This can result in a loss in capacity and early battery failure.

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