iPhone 5S Battery percentage jumps, even with new Battery

Hello,

I have a customer here, he has a device with no damage whatsoever, all i did was change the battery and the Display, now the battery is going haywire, i sent him off with a completely new device, no scratches or dents. new Display and battery, i thought, okay i made some profit, cool and good. after he got back to his home he called and told me: “THE BATTERY IS DOING SOME WEIRD $@$*!” i was like: WHAT how?? i replaced it! he said that he’s gonna come again and give my the device. i took a look, replaced the battery with a different one, same problem! i put the old one in ( which i wrecked ) same problem, how can this be, that 2 completely new batteries and the old one have the same problem, the board is completely fine, heres the problem:

Turn on, Battery at 1%, plug in: Battery Jumps to 31%, plug out, Jumps to 44%, plug in: suddenly 100%, i did a complete reset and stuff with software, nothing helped.

every now and then the battery hits 0% and it shuts off, funny part: without warning

also while charging

really frustrating…

Another funny thing *laughs while crying* :

it works completely fine in DFU mode or Recovery Mode, like no crashes or anything.

i asked the company that sent me one of the iPhone 5S Batteries to send me a new one, they agreed.