The capacity of a storage battery is measured in ampere-hours. One ampere hour is defined as a current flow of one ampere for a period of one hour. Five ampere-hours means a current flow of one ampere for five hours, a current flow of 2 1/2 ampere for 2 hours, or any multiple of current and time that will result in five. This relationship can be expressed as follows: Capacity (In ampere hours)= I*T. Where I is the current (in amperes) and T is the time (in hours). The capacity of a storage battery is usually based on a given discharge rate, since the capacity will vary with the rate of discharge. The capacity of an aircraft battery is usually based on a one hour discharge rate. A 17 ampere hour battery will supply a current of approximately 17 amperes for a period of one hour. A 34 ampere battery will deliver twice that amount of current over the same period of time. If a very heavy load is applied to the battery, it may become discharged in a few minutes.