AA battery: (Wikipedia)
devices designed for AA cells will usually only take 1.2–1.5 V unless specified by the manufacturer. (...)
Rechargeable batteries in the AA size are available in multiple chemistries: nickel–cadmium (NiCd) with a capacity of roughly 600–1,000 mAh,nickel–metal hydride (NiMH) in various capacities of 600–2,750 mAh and lithium-ion. NiCd and NIMH provide 1.2 V; lithium-ion chemistry has a nominal voltage of 3.6–3.7 volts, and AA-sized cells of this voltage are coded 14500 rather than AA.