"battery backup" means having a spare power source that can be used when the main power supply goes out. It allows devices or systems to keep running even during a power outage. Full definition
We have chosen phones which have best battery backup with great performance. (suggestphone.com)
We got a decent battery backup of up to 1 day even for more than heavy usage. (phoneradar.com)
Right now gas powered cars are getting increasingly fuel efficient and electric cars with battery backup in the home and solar on the roof will defeat any attempt at raising prices. (oilprice.com)