AA sized lithium tend te be too high of a voltage (straight up 3.7V) or stepped down, but still a little off.

Personally i'm phasing out AA/AAA sized batteries. They are only for things like bike lights, computers mouses, etc. Those run on mine supply of Eneloops NiMH's. The rest is getting replaced by Lithium based items. Either build in or accepting lithium cells.