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  • Yakub Ansari

Why does a lead-acid battery self-discharge?

Have you ever wondered why your lead-acid battery gets discharged even when not in use? And why unused Lead-acid batteries are required to recharge after every few months. Not only flooded lead-acid batteries but even AGM and Gel type lead-acid batteries also get discharged. And the reason behind it same for all types of lead-acid batteries. In this blog, you will get all these answers.

Why does a lead-acid battery self-discharge?

All Lead-acid batteries- even when unused, discharge slowly but continuously by a phenomenon called self-discharge. This energy loss is due to local action inside the battery & depends on the level of minute impurities in battery elements & accuracy of manufacturing process control. A rise in the operating temperature is an external factor which increases the self-discharge loss.

Self-discharge loss is measured by the “Retention of charge test” which checks the amount of charge retained by a battery after freestanding for 28 days at a standard temperature.

The R.O.C test as per IS 15549 for VRLA battery and IS13369 for flooded tubular Monobloc’s accepts self-discharge loss within 10% & 5% respectively, for a new battery.

You can safely ascertain that the quality of material used & the manufacturing process control is good, simply by ensuring that the batteries meet the ROC limits as per the BIS above. A battery with poor R.O.C can have multiple deficiencies (by way of raw material input or manufacturing defects) inside and the self-discharge loss can grow by 3 or 4 times over the period of its lifetime.


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How to stop battery self-discharge?

You can't stop the self-discharge of the battery, however the same can be minimised by storing the battery in a dry room at an ambient [room] temperature of a maximum of 25 degrees celsius and by avoiding high temperatures as well as direct sunlight.

How retain the self-discharge loss of lead-acid battery?

Self-discharge loss of a fully charged lead-acid battery, as explained above can be replenished by applying a voltage of 2.25 volts/cell across the battery, for example, 2.25 Vpc X 24 = 54 volts for a 48-volt battery.