In engineering, efficiency is a measure of the effectiveness of a conversion process. For battery applications in particular, the achieved efficiency η is of great interest to the user. For a motor, efficiency is calculated from the delivered mechanical output power and the received electrical power. For the efficiency, η = Poutput/Pinput . It is a dimensionless value and changes with the capacity utilization of the machine.
If multiple units, such as motor and gearhead, are arranged in series in a drive train, the individual efficiencies are multiplied together to yield the total efficiency ηtot = η1 x η2 x … ηn.