AA batteries / rechargeable batteries are slightly larger or longer than C-cells. With this adapter it will work, if necessary, in succession in a single unit with one or two C-cells. If there are several C-cells in series (one after the other), there could be problems, especially with fixed C batteries. Then there is a length difference. No idea what SANYO was thinking. But that's definitely not a complete replacement for C-batteries / rechargeable batteries !! I'm a bit disappointed. With a bit fiddly job to do it. Also the use of a single C-Zette ... :-(