AA is the standard size of any battery. These are generally used in portable devices. Their terminal voltage and also capacity depends upon their cell chemistry. Even rechargeable batteries are made in this size. Rating of the rechargeable battery capacity is done in terms of mAH (milliampere-hours). C defines the total capacity of a battery that is whether it can supply C mA for 1 hour, or 3C for 30 minutes etc.
AA rechargeable batteries and charger in the capacity of 500 to 1100 mAh are available which are made up of nickel cadmium, as also nickel metal hydride.
Rechargeable aa batteries supply 1.2 V which is lower than the non rechargeable ones and hence they can not be used for some e devices. Nowadays aa rechargeable batteries and charger of Li-ion chemistry been introduced which are rated at 3.6 V and are compatible with most of the devices.
Aa nimh battery chargers are the ones which are suitable for most of the aa batteries. Generally Aa nimh battery chargers are expensive than the cheap chargers that are supplied with the batteries. These tend to incorrectly charge the cells shortening their shelf life. Aa nimh rechargeable batteries and charger fill in the slot of intelligent batteries and chargers because of the fact that they are designed for the high current as well as applications of rapid charge like racing car models and cordless tools.
Rechargeable aa batteries and chargers which are made up of nimh are generally expensive and at tines even difficult to purchase. But now you can purchase any variant of aa rechargeable batteries and chargers online.