Hi
Depending on the age of the power bank the battery’s can die for good and will need replacing (even lithium ones)
So unless the charging port is damaged or is full of dust and debris (can be easily removed with a sewing needle)it’s probably the battery’s
So my advise would be replace the battery’s and if that’s not a option sell it on eBay to someone who can fix it so it doesn’t end up in land fill and buy and new or used one
Hopefully I answered your question
If you have any more questions please let me know
Thanks:)