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.
I should have brought a portable battery charger.
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.
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.
Do you have a portable charger?
This portable charger has a large capacity.