Why is a battery rated in Ahand not in VA?

Batteries are rated in Ampere-hour because it indicates the amount of charge (discharge current and time) it can deliver.

The amount of available charge is the capacity of a cell or battery which may be expressed in Ah (Ampere-hour).

Battery stores charge in the form of chemical energy and then converts it into electrical energy to utilize for a specific time.

The capacity of a battery is measured in terms of Ampere-hours (Ah) because it represents the amount of charge that is currently available.

A battery stores charge in the form of chemical energy, which it then transforms into electrical energy to use for a specific amount of time.