Primary Cell - Comparison With Rechargeables

Comparison With Rechargeables

Rechargeable batteries are economical to use when their initially higher cost and cost of a charging system can be spread out over many use cycles; for example, in hand-held power tools, it would be very costly to replace a high-capacity primary battery pack every few hours of use.

Primary batteries are useful where long periods of storage are required; a primary battery can be constructed to have a lower self-discharge rate than a rechargeable battery, so all its capacity is available for useful purposes. Applications that require a small current for a long time, for example a smoke detector, also use primary batteries since the self-discharge current of a rechargeable battery would exceed the load current and limit service time to a few days or weeks. For example, a flashlight used for emergencies must work when needed, even if it has sat on a shelf for a long time. Primary cells are also more cost-efficient in this case, as rechargeable batteries would use only a small fraction of available recharge cycles. Reserve batteries achieve very long storage time (on the order of 10 years or more) without loss of capacity, by physically separating the components of the battery and only assembling them at the time of use. Such constructions are expensive but are found in applications like munitions, which may be stored for years before use.