One Trolley Accumulator (upper picture) is believed to be the older, has a manual towing handle and pneumatic tyres
The other Trolley Accumulator (lower right picture) is believed to be the newer. It has a towing handle so that it can be towed behind a tractor and solid tyres.
Each Trolley Accumulator has a metal framed wooden box containing lead-acid cells with a small petrol engine and generator on the top ((lower left picture). The cable connects to the battery socket on the aircraft,