The abbreviation mAH is short for milliampere hour. This unit is commonly used in measuring the total charge of a battery and how long a battery can last when powering a device before the battery requires either disposal or recharging.
A milliampere hour is 1/1,000 of an ampere hour. An ampere hour is the product of a battery's flow in amperes times its time of discharge in hours. For example, a battery that can discharge at five amps for 20 hours is rated with a capacity of 100 ampere hours.
Some commonly used consumer batteries such as AA alkaline batteries do not always use their full capacity when powering devices, and oftentimes these batteries can only use close to their full capacity when discharged slowly. Therefore, while a higher mAH rating implies longer battery life for powering devices, in practice this is not always the case. For powering high-drain devices such as digital cameras, NiMH batteries often use a greater percentage of their total capacity than standard alkaline batteries do.