Nexus 5X not turning on... until it does

[Android Central Question]

So yesterday my good old 5X suddenl went pitch black. Thought the main board died, which is a common problem with this device, but then suddenly 5 or 6 hours later the red LED starts to blink letting me know the battery is dead. I put my charger in, and it started charging with the display turning on. I tried to go to boot menu for some recovery, but the nit died off again pitch black. No LEDs, no button does anything, no charging. And again, around 2-3 hours later it turned on, but died again.

Now i know it's most likely some hardware failure, but it looks like the board is not completely boinkers.

Where should i start inspecting in such a scenario?

Thanks!