A load handling device (130) for lifting and moving one or more containers stacked in a storage system comprising a grid framework structure supporting a plurality of tracks arranged in a grid pattern to define a grid structure above the one or more stacks of containers, the grid pattern comprising a plurality of grid cells, the load handling device comprising: A) a driving mechanism operatively arranged for moving the load handling device (130) on the grid structure, B) a vehicle body (132) housing: i) a container receiving space (152) located above the tracks; ii) a lifting device comprising a lifting drive assembly (140) and a grabber device (139) configured, in use, to releasably grip a container and lift the container from the stack into the container receiving space, iii) a cassette (142) housing a rechargeable power source for powering the driving mechanism; wherein the load handling device 130 comprises a thermal management system comprising a temperature sensor and at least one temperature regulating device configured to maintain the temperature of the rechargeable power source within a predetermined temperature range in response to a signal from the temperature sensor.