Don't quote capacity. It is the correct tern, physically. Capacity is the amount of electrical charge something can store, Ah is unit of that. Not the natural unit though, that would be Coulomb (C).
Why use Charge and not energy? Because the voltage changes as the battery is discharging, so it's not as straight forward as just multiplying with the voltage.
Why use Charge and not energy? Because the voltage changes as the battery is discharging, so it's not as straight forward as just multiplying with the voltage.