The present invention provides an estimate of the amount of time left on the battery by monitoring not only the voltage available from the battery, but also the amount of current flowing from the battery. It has been found that periodic sampling of the battery voltage and current drain enables accurate battery monitoring. The sampling technique alternates between sampling battery voltage and sampling current drain. An electric circuit is provided which enables the cost-effective sampling to occur. A method is then applied to the sampling signals by a microprocessor which determines the amount of time left under battery power. In a preferred embodiment, a graphic representation is provided of the amount of battery time left.