The number of ampere-hours that a battery can supply at a given rate of current flow after being fully charged. e.g., a battery may be capable of supplying 8 amperes of current for 10 hours before it is exhausted. Its capacity is 80-ampere hours at the 10 hours rate of current flow. It is necessary to state the rate of flow, since same battery if discharged at 20 amperes would not last for 4 hours but for a shorter period, say 3 hours. Hence, its capacity at the 3 hour rate would be 3x20=60 ampere hours.