The present disclosure relates to a method for powering up a medical device powered by a battery. The method includes executing an initial battery test. In the initial battery test, a difference voltage between a battery voltage measured without and with a test load is determined. The test load is favorably dimensioned not to significantly stress the battery. The difference voltage is compared with a difference voltage threshold, the difference voltage threshold being predefined in dependence of the no-test-load voltage. The method further includes providing an alarm if the difference voltage is above the difference voltage threshold. The present disclosure further concerns a medical device that implements the method and a method for determining the relation between the difference voltage and the difference voltage threshold. The disclosure can be used to ensure that an alarm is provided if a newly inserted battery is too weak to power the medical device.