A battery pack management system provides information such as remaining capacity and/or run time to empty for a battery. A time taken for a battery voltage to drop a threshold amount is measured and used to determine a remaining capacity of the battery. The time may be associated with a temperature and current of the battery. The remaining capacity of a battery is calculated by monitoring a discharge of the battery. For example, current drawn from the battery is monitored over a period of time and an initial amount by which the battery has been discharged is calculated. Compensation of this initial amount is carried out in order to take into account factors such as temperature, self-discharge rate and age of the battery.