also: せかんどばってり
noun
second battery; backup battery
Refers to an additional or spare battery, often used in devices like cameras, laptops, or electric vehicles to extend runtime or provide backup power.
このカメラにはセカンドバッテリーが付属しています。
This camera comes with a second battery.
長時間の撮影にはセカンドバッテリーが必要だ。
A backup battery is necessary for long shooting sessions.
予備バッテリー also means 'spare battery' but is more general; セカンドバッテリー often implies a second battery that is used in rotation or as a backup, and is more common in technical product descriptions.
Loanword from English 'second battery'.