Prolonging The Life of Rechargeable Batteries

Don Bradbury offers some general recommendations on extending the life of rechargeable batteries

When a rechargeable battery is first bought, it will usually come with a certain amount of charge in it. Don't use this charge, except perhaps to check for a short time that any equipment you bought with it actually starts and runs.

The main thing you should do with the battery is test your patience by spending the time necessary to charge the battery to full capacity, as recommended by the manufacturer, having due attention to the type of charger you use and the length of time the cell should be on charge.

If you should have early types of rechargeables, such as NiCad - and possibly also NiMH, though prevailing wisdom is uncertain on the matter in their case - the next thing to do is run them down under working conditions to the lowest state of charge you can manage (that is, while keeping an eye on proceedings) without letting the battery go profoundly flat, ie to having no charge left at all. Then fully charge the battery again as soon as you can. This run-down and top-up process should ideally be repeated two or three times.

This is to maximise the 'memory' of the battery, which is the property of such a cell to remember the charge capacity it is intended to hold. To be on the safe side, do it with any type of rechargeable you get. Batteries initially retain this memory but tend to slowly forget it over time, the capacity to hold full charge slowly fading with usage.

Modern rechargeable batteries, such as Lithium Ion, should then be used under the intended working conditions but, again, these conditions should never allow the cell to drain to the point of being 'profoundly flat', ie with essentially zero voltage output. Under prolonged storage conditions, and especially if the equipment that the battery runs in is left switched to the running position, charge drainage to essentially zero volts will take the chemistry of the battery to a state where it, in effect, cannot remember what it is supposed to do! It will, thereafter, take no further charge and the battery will be fit only for disposal.

Now, we have known such badly handled batteries that were kicked back into action, so to speak, by a routine of constantly switching on and off the charger every few seconds for a period, after which a substantial proportion of the design charge might be finally taken.

Such rescue operations are, however, rarely successful in our experience, so do remember to switch off the equipment housing the battery after use, and preferably remove the battery from the equipment's battery housing for storage, taking care to avoid shorting the battery terminals with anything that can conduct electricity. These are usually metallic objects, but even a poor conductor will discharge a cell over time.

Try to leave the battery, while in prolonged store, with a charge of about one quarter of maximum. Left flat, the battery will be in danger. Left fully charged, the battery may suffer from reduced capacity thereafter.

And finally, you should periodically put an amount of charge back into a stored battery to replace that which is lost by self-discharge, which results from the capability of the cell to form a discharge circuit within itself, ie with no external connections. This self-discharge can run a cell down to essentially zero voltage within weeks in certain equipment, rendering it useless. We've suffered from this ourselves, and it's painful on the pocket!

Finally

These are all councils of perfection, we know, but rechargeable battery cells are not cheap; they deserve the best of attention if they are to give you good, prolonged service.

Don Bradbury