The majority of electronic cigarettes contain a rechargeable battery and are either inbuilt or they need to be inserted into the device. These batteries are typically lithium ion ones.

There are a lot of counterfeit AW batteries circulating the market at the moment. Fake batteries can be very dangerous, as they are often untested and their chemistry and performance is unknown.
There are two types of batteries: manual and automatic. Manual batteries require a button to be pressed, whereas automatic batteries operate without through a internal sensor. Most Mods require high drain rechargeable batteries to power them.