sparebattery
nounUK /ˌspeə ˈbætəri/
US /ˌsper ˈbætəri/
An extra battery you keep to use when your first one runs out.
I packed a spare battery for my camera before the trip.
OTHER MEANINGS
2. A second battery kept in a vehicle in case the main one fails.
He keeps a spare battery in the trunk for emergencies.
3. An additional battery for a phone or laptop carried while traveling.
Always carry a spare battery on long flights.
4. A backup power source for a device that must keep running.
The hospital keeps a spare battery for the life-support monitor.