1. A device comprising:first terminals to couple with a first battery arranged to supply power to the device, the first terminals including a positive terminal for coupling with a positive contact of the first battery and a negative terminal for coupling with a negative contact of the first battery;
a first winding and a second winding that are arranged to be inductively coupled;
a transistor having a base, an emitter, and a collector, wherein the base is coupled to the positive terminal through the first winding, the collector is coupled to the positive terminal through the second winding, and the emitter is coupled to the negative terminal, wherein the first winding and the second winding are coupled to the positive terminal with opposite polarity;
a light emitting diode (LED); and
second terminals to couple with a second battery to be charged by the device,
wherein the device is arranged to couple the LED and the second battery in series with each other, with the LED and second battery being coupled in parallel with the second winding, and
wherein the LED is arranged to be reverse biased with respect to the first battery and the second battery.