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Q: Can I extend the storage life of my torch’s batteries by keeping them in the refrigerator?

A: Primary batteries such as the Leclanché (zinc-carbon) or alkaline-manganese systems can have their storage lives extended significantly by storage at 0 °C. For such cells, the loss of capacity on open circuit is caused mainly by chemical side reactions such as zinc corrosion. Such processes, like chemical reactions in general, are accelerated by a rise in temperature. Water loss is affected similarly.

For a Leclanché cell stored at room temperature the capacity will fall to about 90 per cent after a year, to 70 per cent after two, and to 40 per cent after three. At the much higher temperature of 45 °C, it will have its capacity reduced to 20 per cent after only a year. However, at −20 °C the capacity will have fallen to some 80 per cent after 10 years. Therefore, it is best to store such batteries in a refrigerator. Keeping them in a deep freeze, however, could damage the batteries if the can and seals have significantly different coefficients of expansion.

Lithium batteries have longer shelf lives because when the shell is filled during manufacture, the lithium anode reacts rapidly with the electrolyte to form a compact passivating layer. This virtually stops further corrosion. Even when stored at room temperature, they can retain up to 90 per cent of capacity after 10 years. Some cells (lithium-sulphur dioxide, for example) retain more than 70 per cent of their full capacity even after a year’s storage at 70 °C.

In contrast, aqueous secondary cells have very poor charge retention -especially nickel-cadmium and nickel-metal hydride batteries. At room temperature the available energy of a recharged battery drops to about 50 per cent after six months’ storage for new, low-discharge rate, sealed cells and to even lower values for cells which are high-power or which have been cycled many times. Again this loss may be reduced to about half of the room temperature amount by storing the charged cell in a refrigerator. Better still, keep such batteries connected to an appropriate charger when not in use.