How do you calculate the capacity of a battery?

The capacity of a battery can be calculated by measuring the current and time it outputs. The specific calculation is as follows:
Battery capacity = current x time
In the base, the current is usually expressed in amps (A) and the time is usually expressed in hours (h).
For example, if we test a battery that can supply power for 4 hours at a constant current of 1A, the capacity of the battery is:
Capacity = 1Ax4h = 4Ah
It should be noted that in actual use, the output current of the battery may be different, and the power provided by the battery will be different under different currents. Therefore, the battery capacity is not completely accurate and can only be used as an approximation.