We have had a few storms come through the Twin cities recently. Occasionally these storms take out the power in various areas.
This can affect your building in a couple of areas. One of those could be the access systems that keep your doors locked after hours. Having the system on a battery backup will keep the doors locked on systems with magnetic locks. It will also allow the system to continue to run and allow the card readers to continue operated and let your tenants into the building if needed. The second item would be EMS systems that control the HVAC systems in a building. Once power is restored the EMS system will should bring the building back to the temperatures it has programmed into it. These backup batteries should be checked yearly at the very least. I would recommend twice a year.
Some larger buildings and certain companies have large backup generators that power the entire building. These should be tested and ran once year.