Brick type airsoft batteries are typically designed to fit into airsoft guns that use AEG (automatic electric gun) systems.
These batteries are called "brick" type because they are shaped like a rectangular block, Brick type airsoft batteries are typically made of Li-Po (lithium-polymer), lithium-ion or NiMH (nickel-metal hydride) cells, and are available in a range of voltages and capacities to suit the needs of different airsoft guns. It's important to note that different airsoft guns have differently shaped battery compartments and may not be compatible with all types of batteries. It's always a good idea to check the manufacturer's recommendations or consult with an airsoft expert to get the correct airsoft battery for your gun. Li-Po batteries are normally smaller in size than a NiMH.