Disclosed herein, among other things, are apparatus and methods for detecting and switching battery polarity in a battery charger. In various embodiments, a method includes grounding a first terminal of a battery inserted in a charger and sensing a bipolar voltage from a second terminal of the battery. The bipolar voltage is converted to a reduced unipolar voltage for sensing by an input to a microcontroller. A low resistance analog switch connects the battery to a charging circuit. The switch state of the analog switch is controlled using an output of the microcontroller, to present the proper battery polarity to the charging circuit based on the unipolar voltage. The battery is charged using the charging circuit, in various embodiments.