Translation guide
A portable battery charger is a device used to recharge electronic devices on the go. In Japanese, the most common term is モバイルバッテリー, a loanword from English. Other terms exist but are less common or more technical.
A portable device that stores electrical energy and can charge smartphones, tablets, etc., without a wall outlet.
The most common and widely understood term. It is a katakana loanword from English 'mobile battery'. Used in everyday conversation, advertising, and product descriptions.
モバイルバッテリーを持ってくればよかった。
I should have brought a portable battery charger.
このモバイルバッテリーはスマホを3回充電できます。
This portable battery charger can charge a smartphone three times.
Literally 'portable charger'. This term is also used, but less frequently than モバイルバッテリー. It can sound slightly more formal or technical.
携帯充電器をお持ちですか？
Do you have a portable charger?
Uses the English loanword 'portable' plus 'charger'. Less common than モバイルバッテリー, but may appear in product names or technical contexts.
このポータブル充電器は大容量です。
This portable charger has a large capacity.