Depend on the model. Most good models DON'T need a battery. A good shime will use the sector, with, maybe, a backup battery in case of power failure.
It may be a deffective door bell button. Very easy to change, LOT of models available.
It can be a tripped breaker or blown fuse. Rest the breaker or change the fuse.
It can be faulty whiring. This can cause the breaker to trip or a fuse to blow. Call an electrician to check the whiring.
Electro, April 2014