The power supply to the hearing aid is derived from its battery. Hearing aid batteries used currently are of 2 main types, zinc-air and mercury, although most in use today are zinc-air cells.

The primary feature of the zinc-air cell is its longer shelf life compared to the mercury- or silver-based hearing aid batteries. Zinc-air cells are not activated until a tape seal is removed from the positive side of the battery. This side contains small holes through which air enters to initiate activation. In most situations, the zinc-air cells last longer than their mercury counterparts.

Hearing aid batteries have a relatively flat discharge rate, and the battery's capacity is rated in milliampere hours (mAh). If the current drain of a hearing aid is known, an estimate of the expected life of the battery can be calculated by dividing the battery's capacity by the current drain measured in milliamperes (mA).

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