Replacement battery issue - not charging/shutting down.

I’ve got a bunch of iPhone 6S’s that I have been replacing the batteries in. Some, they work absolutely flawlessly and behave exactly as you’d expect. Some are working when I initially install them into the phone to check they are working properly before sticking the pull tabs onto the battery.

Once I’ve stuck the pull tabs on and reinstall the battery, it takes slightly longer than usual when holding down the power button for the phone to boot, and once it does it sits at 1% for a few seconds then jumps around. It also won’t charge and will randomly shut down. Battery health on iOS says it needs servicing despite it being a brand new battery. This is the same battery that when I initially slotted it into the phone to check it was all OK was reading as 100% in battery health. I’ve checked in 3utools and the phone seems to think its the same battery that was installed in it originally (same serial number.)

Other 6S’s I’ve done have come up with a different battery serial and these are the ones that work fine. What’s going on here? Battery issue or phone issue, and can it be rectified? (Pointing out all batteries are from the same vendor.)