There are a few different types of batteries being used in electric airplanes today. Some are used more than others as technology advances and better batteries are made but here are the basic types:
NiCad (Nickel Cadmium):
these are of the first rechargeable batteries that were used in electric airplanes and are not the most popular primary source of power anymore.
NiMH (Nickel-Metal Hydride):
These batteries were an improvement on the older NiCad batteries and are still often used as receiver batteries and to power a transmitter but even these are beginning to get used less and less.