[Q] Phone keeps rebooting at LG logo without a charger

Hello everybody at the LG G3 part of XDA,

A friend of mine has an LG G3 and his phone broke. So he asked me to fix it. I myself am an Oneplus One user.

So the problem is really simple to explain. The phone doesn't work when there isn't a charger plugged in. When there is a charger plugged in everything is fine and the phone works normally.

So my friend tried to downgrade from lollipop to kitkat ( I don't know what he exactly did ). He doesn't have much knowledge about phones so ofcourse it went wrong.

Here is a video of what happens.
https://www.youtube.com/watch?v=VP8MUPsANes

I already did a full reset with the LG flash tool and put the stock 4.4.2 Kitkat rom on it.

I have also checked the battery and it has a normal voltage of 3.8v. My friend also told me that he already swapped the battery in a store.

I do not know anything about a stock recovery of an LG G3, but I tried to acces it and I could get in to the hard reset screen but when opted Yes for everything it got stuck in that same "bootloop". When the phone is in the Hard reset menu then it wil stay ON without a charger. In all other cases it wil stay in a "bootloop"

I asked another friend of mine who has a lot of experience with phones. He said that it might have something to do with the a file that keeps the battery in check in the bootloader or the recovery, but he wasn't sure which one.