Just a FYI, but rechargeable AAs batteries have a nominal voltage of 1.2v, but when fully charged they charge up to more like 1.4v. In just the same way that Lipos have a nominal 3.7v per cell, but charge up to 4.2v per cell. They will drop down to 1.2v reasonably quickly, but then hold it a lot better than normal AAs. I'd recommend any of the newer pre-charged AAs rechargeables (Eneloops being my preferred type), they hold their charge for a long time, and have excellent capacity.