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Battery: Convert Charge and Energy

Calculator for charge in ampere hours, energy in watt hours and voltage. Batteries often only specify their nominal charge and nominal voltage. The charge is sometimes referred to as capacity. Strictly speaking, however, capacity refers to the usable charge, which is not quite the same as the theoretically maximum charge. Anyway, the more important value for practical battery size is the electrical energy. This is calculated as charge multiplied by voltage. In everyday language, energy indicates how much electricity can be drawn from a battery.

Nominal charge Q:		coulomb C, Asmilliampere hours mAhampere hours Ah
Voltage U:		millivolts mVvolts V
Energy E:		joules J, Wsmilliwatt hours mWhwatt hours Whkilowatt hours kWh

Please choose the units, then enter two values, the third value will be calculated.

Formula: E = Q * U

Example: with a nominal charge of 20000 milliampere hours and a voltage of 5 volts, the battery has an energy of 100 watt hours when it is fully charged.

Electrical energy is measured in watt-hours and derived units such as kilowatt-hours. It describes how much work a battery can perform. This energy is calculated by multiplying charge, given in ampere-hours, and voltage, given in volts. Since amperes times volts equals watts, the result is watt-hours. While charge indicates how many electrons a battery can theoretically store, voltage indicates the drive with which these electrons flow. Energy is therefore the crucial value for evaluating a battery's actual performance. Over time, the usable charge decreases due to aging, temperature, or frequent charging cycles, a process known as degradation. This also reduces the available energy until the battery eventually no longer functions adequately. A rechargable battery's lifespan depends heavily on usage and maintenance, but at some point, replacement becomes unavoidable. Old batteries that can no longer be used still contain the same amount of essential raw materials as at the beginning, often lithium. Therefore, they should be recycled.

Last updated on 12/12/2025. Author: Jürgen Kummer

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