AA batteries are usually in the 1.2V to 1.5V range, depending on the exact battery chemistry. For example, Nickel-Cadmium ...
It contains two Sanyo 2100mAh NiMH AA rechargeables (Model HR-3U 1.2V). In addition to that, there is an Atmel microcontroller (not pictured) and the copper temperature probe you can see above.