Most modern day gate & garage motors have battery back up in case of power failure. Some depend on the battery to operate and others don’t. The models that depend on the battery only use main power to keep the battery charged. Other models will run on mains and switch over to battery during mains failure.
Batteries should be checked every 6 months or so. Switch of the unit and simulate a mains failure to check battery operation. Battery life vary but in most cases they will need replacing every 2 to 3 years.
Most commonly Used battery is the 12v 7 aH Battery