Battery capacity ($Q=\int Idt$)

Battery capacity is the amount of electric charge delivered between specified charged and discharged states under stated conditions. It is $Q=\int I(t)dt$, commonly reported in ampere-hours; $1\mathrm{Ah}=3600\mathrm{C}$.

Capacity is distinct from delivered energy, which is $\int V(t)I(t)dt$. Two batteries with equal ampere-hour ratings can deliver different energies because their voltages differ. Discharge rate, temperature, endpoint voltage and aging affect the measured capacity. Comparing ratings therefore requires the same test conditions and a stated choice of active-material or full-device mass when using specific capacity.