Photo 1—The internal charging unit (ICU) is on the left. The external charging unit  (ECU) is on the right. Power is applied to the ECU via a wall plug supply. Energy is inductively coupled from the ECU across the gap between the transinductors, and the ICU processes it to charge the AA battery packs. The boards also include Radiotronix EWD-900-HDTC radios and 900-MHz antennas. (These were for the telemetry application and aren’t documented in the text.)