Why Battery rating 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 tofully 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 1018electrons, 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