LG G2 doesn't boot and flashes 8 times red after repair

Dear fellow XDA members,

Yesterday, I replaced by LG G2 screen and after the repair the phone wouldn't boot anymore. It however shows signs of life if I plug in the charger, this is what happens then:

Notification light blinks 8 times red
Pause
8 times a red blink
Pause
and this continues for ages.

What I did sofar:
-Tried to soft reset & hard reset via button combo (no result)
-plug out the battery connector & plug it in again
-check all connections and possible damage (no potential problems found)
-Check voltage of battery (it is around 3V)
-Put phone in charger for a whole night

Do you guys have any ideas what is causing the problem? what does the 8 blinks error code mean? Hopefully you can help me out!

z3c won't turn on. Flashes battery charging screen when plugged in to the wall.

I just replaced the cracked screen on my z3 compact but the phone won't turn on, and when I plug it in to charge, it flashes the battery icon. When I plug it into my pc, windows makes a noise, but won't recognize the phone.

I followed a guide from ifixit and an accompanying youtube video.

Neither of them removed the battery before changing the screen connector, but people were telling me that may have fired the phone?

Is it for sure bricked?