A rechargeable battery allows the mobile use of a telescope with a motorized mount. In astronomy, the term power tank is also commonly used.
Most astronomical mounts already have a power cable with a DC power plug (cigarette lighter cable) which can be used to connect them to a car battery. For this reason power tanks have suitable sockets or adapters for these plugs. This means that you do not need long cable to reach the car, and you preserve your car battery.
In addition to this 12-volt power supply, power tanks also offer USB outputs for other accessories that can be operated with 5 volts.
In addition to the large power tanks, you will also find smaller power storage units for various accessories under the heading "battery packs".