also: モバイルバッテリ
noun
portable battery charger; power bank; external battery
A portable rechargeable battery used to charge mobile devices like smartphones and tablets. Common everyday term.
from English mobile battery
旅行のときはいつもモバイルバッテリーを持っていく。
I always take a power bank with me when I travel.
スマホの充電が切れそうだったので、モバイルバッテリーを使った。
My smartphone was about to die, so I used my portable charger.
Loanword from English 'mobile battery', referring to a portable power source for electronic devices.