iPhone 5s boot loop and wont turn on,only when connected to wall charger

Hi all,
I have a very strange problem.
My iPhone 5s is not powering on when not connected to the wall charger even with a new fully charged battery.
When I plug it on the wall charger it goes in an infinite boot loop and when I unplugged it, it just turns off.
I have check the battery connector pins and there is no voltage when it is plugged to the wall charge. I cannot even find any voltage on the small compounds close to the connector.
Could it be the U2 IC which is dead? I would have expected the phone to turn on with a new component.
Thanks in advance for your help! I am totally lost.