No signs of life whatsoever

So my friend has dropped their iPhone 8 and it is not turning on at all. Back seems severely cracked and front screen has only a few cracks. I've tried plugging it into the charger with a battery activation board and at first it showed a red light, but plugging it back in the second time, it began to accept some charge for a short time, then no current or voltage. The power and volume buttons of course wouldn't do anything to contribute turning it on. The battery however does still work and can be charged externally.

Summary, no power whatsoever. What could be the problem? And which area should I check, especially where on the logic board?