Backup power is a reserve supply for when the main one stops. Switch to backup power.
A hospital tests its generators regularly, because the failure you find in an emergency is too late. Backup power usually fails for want of fuel or a flat starter battery rather than the generator.
1nounbackup powerA reserve supply for when the main one stops.
“The backup power carried the theatre through the whole outage.”
backup power is a supply.
Practised in Emergency & Rescue