A battery unit including a battery (3) is equipped with a monitoring circuit (9) for detecting and evaluating operating variables related to charge state of the battery (3). So that energy is not drawn from the battery (3) by its own monitoring circuit (9) when an external load (2) powered by the battery unit is shut off, the supply of electrical power to the monitoring circuit (9) in the battery unit is disconnected, either immediately or after a certain time delay, when the load (2) is shut off. This slows the discharge of the battery (3) when it is not supplying electrical to the load (2).