It is a measure of electric current; one A of current represents one coulomb of electrical charge moving past a specific point in one second (1 C/s = 1 A).
Amp Hour Rating
The amp hour (AHr) rating describes the size of this storage capacity of a battery over a period of time. A battery with a 125 AHr rating over 20 hours means it can supply 6.25 Amps of current for a period of twenty hours before it is 100% discharged. More Ampere hours can be drawn from a battery if the current drawn from the battery is low. Some battery companies name their battery models and publishes their 100 Ahr ratings, however most provide a 20hr rating. This rating as it implies, is the amount of ampre hours that can be drawn from a battery.
It is a group of batteries wired in series or parallel (or both), to store the electrical energy produced for later usage.
Battery Available Capacity
The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions including discharge rate, temperature, initial state of charge, age, and cut-off voltage (also see amp hour rating).
It is the most basic individual component of a storage battery. They consist of one or more positive electrodes or plates, an electrolyte that permits ionic conduction, one or more negative electrodes or plates, separators between plates of opposite polarity, and a container for the above.