Why Battery rated in Ah (Ampere hour) and not in VA. ?

Battery stores charge in the form of chemical energy and then converts it into electrical energy to utilize for a specific time. The amount of available charge is the capacity of a cell or battery which may be expressed in Ah (Ampere-hour). Moreover, in a charged battery, the numbers of molecules are limited to create a flow of electron in electric circuits, so, there must be a limited number of electrons in a cell/battery which they motivate through a circuit to fully discharge.

Now we have the option to rate the battery capacity in Number of flowing electrons for a specific time, but, it would be a headache, because there are a vast number of electrons in it.  So we have another option (1C (Coulomb) = 6.25 x 1018 electrons, or 6,250,000,000,000,000,000 electrons.

In addition, 1A (Ampere) = 1 coulomb of electrons per second and,

1h = 3600 Seconds

Therefore;

1Ah = (1A) x (3600s) = (C/s) x (3600s) = 3600 C.

∴ A (1 Ampere) = 1 Coulomb per second = C/s