There are four main sizes of hearing aid batteries, colour-coded and numbered for easy identification. Manufacturers are also developing even smaller batteries that retain the same power.Blue 675: The largest hearing aid battery, providing the greatest amount of power.Orange 13: Commonly used in smaller behind-the-ear hearing aids and larger in-the-ear models.Brown 312: Similar circumference as the 13 but half the depth, making it slightly fiddlier. Suitable for smaller behind-the-ear aids.Yellow 10: The smallest battery, designed for in-the-canal hearing aids.