Abstract: A charge unit for charging a robotic load handling device operative on a grid framework structure including a plurality of grid members arranged in a grid pattern is provided. The charge unit including a charge providing head for coupling with a charge receiving head of the robotic load handling device, a plurality of profiled sections, and a cartridge for interfacing with a hoist element of the robotic load handling device. The cartridge is moveable along the plurality of profiled sections so as to effect vertical movement of the charge providing head relative to the charge receiving head of the robotic load handling device.