I came across the following when I was reading up about fully drained batteries in phones:
If the phone is OFF for a month, then it is probable that the battery has gone down to a point that the BMS has shut it down. The BMS won't allow you to charge the battery because, in its own assessment, the battery is dead. Best way to test this case is to have another same phone with a good battery (or just a new battery altogether), detach the cable from that and test on yours.
Referring to the above, do Android phones have their BMS as part of their bootloader or kernel? Or is it a part of the Power IC itself?
Are there any safety mechanisms related to booting up a device with fully drained batteries? If so, why?
(Came across something similar)
I've had difficulties with phones in the past after batteries have fully discharged - eg the Moto G5 had some battery protection "feature" that stopped it starting up if it thought the battery was fully discharged - it was a bit over sensitive so would sometimes assume the phone was fully discharged when it wasn't. Try leaving it on charge for 24 hours or so then holding down the power button for for at least 20 seconds with it still on charge.