iPad not charging after battery replacement

Hi Guys, I changed a battery in a iPad Air 2 and it charged fine when it was with my with repair, Customer has come back to me with the below -

Hi Tom

Unfortunately, the ipad refuses to charge now. Have tried various different chargers and leads. (All of which worked for it wore & still work for the iPhone). Also tried a full reboot. It just comes up with charging symbol but gradually loses charge!  Now down to 26% & reducing.  As you an see here, a screenshot done earlier.

Any tips please? Maybe Faulty battery any advise would be really helpful

Thanks

Tom