Trouble with Zenfone 6 battery pack

Bought this for about $18 to replace the bloated battery for the Zenfone 6, now my backup phone.

Quite a chore to mount the battery as this is not a user replaceable battery. The cell works fine but when I put everything back I found that I couldn't get the battery to charge when connected to the mains. Got to open it up again when I can find the time to do some trouble shooting