Battery
Batteries are needed to operate many things, like torches, radios, cameras, tape recorders, cars, clocks.
Batteries can be rechargeable or non-rechargeable. They store Direct Current electicity.
Batteries come in lots of different shapes and sizes and voltage, it is possible, but not easy, to run wires to use an odd size battery for an odd purpose.
Batteries are always more costly/expensive than mains electricity. But mains electricity is not suitable for things that are mobile.
Bicycles have tail lights that can be operated by batteries, and sometimes by a little generator powered by the wheels.
Hand and foot generators can be used to replace batteries, but they can be tiresome.
Wind-up generators are now available to power small clockwork radios, clockwork torches, etc.
Since clockwork clocks have been around for hundreds of years, and batteries for two hundred, it is amazing that no-one thought of a clockwork torch until recently.