standby battery
nounUK /ˈstændbaɪ ˈbætəri/
US /ˈstændbaɪ ˈbætəri/
A standby battery is a backup battery that gives power when the main power stops.
When the electricity went out, the standby battery kept the lights on.
OTHER MEANINGS
2. A battery kept charged and ready to take over automatically if the main power source fails.
The hospital's standby battery kicked in within seconds of the outage.
3. A small battery that keeps a device's memory or clock running when it is switched off.
Replace the standby battery on the motherboard so the computer keeps the correct time.
4. A battery held in reserve for use in an emergency or as a replacement.
We keep a standby battery in the car in case the main one dies.