Logic board defect: iPhone XS Max doesn't charge and stays at 1%

Hi Sem,

Obviously the best path to take is to first find out exactly what's wrong before throwing fixes at the phone.

You said it's been rebooting, which could indicate a sensor problem. There will likely be logs stored in the phone that may point you directly to the actual cause rather than having to speculate. Take a look at @flannelist's Wiki article on Kernel Panics and see if there are any panic logs to be found. If so, post the first page or so of whatever you find and we can see about narrowing down the cause with you.

iPhone Kernel Panics - iFixit

Outside of that, first thing would be to get a new battery and see what effect that has on the whole situation.

Note of caution here; starting with the iPhone XS, Apple has paired the battery with the logic board, meaning you'll get a non-genuine part warning (whether or not you're using genuine Apple parts) plus you'll lose the battery health indicators. The only solution currently available is to cut the BMS, or Battery Management System, off the old battery and spot weld it onto a new cell that comes without the BMS, then go in with a device programmer and manually reset the battery health percentage and cycle count. So even of you don't use it right away, save that old battery in case you ever want to restore that information. Note that the battery will work correctly in all other respects.