Batteries

Capacity

The battery capacity $C$ is often given in $\mathrm{Ah}$ (Ampère hours) or $\mathrm{mAh}$ (milli-Ampère hours).
In fact, the unit $\mathrm{As} = \mathrm{C}$ (Coulomb) is the amount of available electrical charge in the battery.
Example: If a battery of $C = 1\,\mathrm{Ah}$ is discharged with a current of $1\,\mathrm{A}$ then it takes 1 hour until it is discharged.

Discharging a coin cell with different constant resistors. Lower resistance = higher current.
Source: Adafruit

Examples:

$C = 2000\,\mathrm{mAh} = 2\mathrm{Ah} = 2\cdot 3600\,\mathrm{As} = 7200\,\mathrm{C} $
Discharging: The Battery can provide a current of $2\,\mathrm{A}$ for $1\,\mathrm{h}$. But: High discharge currents often lead to a reduced capacity!
Discharge at lower current: $10\,\mathrm{mA}$ for $200\,\mathrm{h}$. The product must be constant.