I think you’re probably right, I had a second go at the contacts this time I got in there with the needle nose and bent them slightly to tighten the contact, (I noticed they were maybe 0.5mm apart at rest) then ran a tiny flat file in and out a few times in each contact which brought one battery back without issue, the other stubbornly wouldn’t charge, until yesterday when I received a brand new DCB-1104, which charged it up without an issue, so maybe there’s an extra little bit of contact resistance on the old chargers, maybe the new charger has different error detection circuitry… Who can say.