In order to avoid reverse insertion of batteries inside battery compartment, please pay attention to the positive (+) and negative (-) marking on battery sleeve. They must match the positive (+) and negative (-) markings on the device. Battery leakage will occur If one of batteries are reversed among three or more batteries connected in series. Leaked electrolyte can corrode the metal housing and battery contact pins of a device, and it can damage the electronic circuitry of your devices.