Apparatus for automatically charging a transponder mounted to a go-cart. The transponder charging unit is basically comprised of a housing having a wall which divides its space into first and second compartments wherein a PC board and a transponder are at least partially contained, respectively. A cover plate secures and protects the PC board and transponder within the housing. A wire is spliced into the go-cart's coil grounding wire to extract A/C power therefrom and send it to the PC board. The PC board contains several solid state devices to rectify and regulate the voltage. Wires extend from the PC board's output to charging contacts operatively connected to the transponder's battery, thereby providing a charge thereto. Thus, the transponder's battery, is continually being charged while the go-cart's engine is running.