reservebattery
nounUK /rɪˈzɜːv ˈbætəri/
US /rɪˈzɜːrv ˈbætəri/
A reserve battery is a backup battery that gives extra power when the main battery runs out.
My flashlight has a reserve battery so it still works when the first battery dies.
RELATED WORDS
OTHER MEANINGS
2. A battery kept charged and ready to start a car or machine if the main one fails.
The hospital's generator has a reserve battery to keep the lights on during a power cut.
3. A small battery inside a device that keeps its clock and settings saved.
The computer's reserve battery keeps the time correct even when it is unplugged.
4. A battery stored for later use instead of being used right away.
We packed a reserve battery in the camping bag for the radio.