iPhone 5s battery stuck at 100% after u2 replacement & q2 jumper

Hello,

i had a family member's iphone 5s that has been used with a bad charger for a long time. The phone would not charge/start if battery was completely dead, and when a full or partially charged battery was placed,the phone would start and accept charge but would discharge quickly after that on its own.

So i ordered a new U2 IC chip and replaced it.

U2 replacement worked fine and the phone would start with a charged battery BUT would not detect the charging cable at all. I think in the process i chiped/damaged the Q2 chip.

So i removed the old Q2 chip and put a jumper in the 3 contact points.

Now phone boots up normally and it detects the cable and charges up fine.

The problem is the battery level reports 100% all the time until it actually runs low after hours(lets say the true percentage is 15%) and starts counting backwards from 99% down to 1% and shuts down.

If I plug the charger in, lets say at 4% ,the percentage will normally start going up until it reaches 100% and stays there, until low-battery of course.

What could be the problem? Could it be a bad q2 jumper? I luck the microscope to see if all 3 points are connected ok, but phone works and charges so I guess they are fine...

Could it be a battery problem or maybe some u2 contact points that haven’t been soldered ok?

What part of the phone is actually responsible for measuring the battery percentage?

Notes: The battery I used was a completly new one.

I put a youtube video to play(and test the battery) and played normally for about 5 hours until it shutdown.Seems normal battery life to me.

I am in NO way professional but i like DIY stuff.I only have a cheap hot air gun and a cheap soldering iron but i luck the microscope for precision.

Thanks in advance.