Problem solved. I removed the bottom cover to look at things and noticed the battery cable had slided like 2 milimeters out of its slot, and that was the cause of the problem. Unfortunately, it doesnt sit tight in the slot (no locks either) so it would probably slide again after some time carrying it around. I solved that with just a small drop of hot glue, so the cable is now secured in place. If I ever want to remove the cable, I can pull the glue out with my fingernails. Thanks for the tips.
I will try to keep it short: - When plugged in, the charging LED indicator is on - Battery charging is stuck at 50% - Bios says battery is "Healthy" - Once the charging cable is unplugged, laptop dies instantly - Laptop doesn't turn on when unplugged   Any ideas? Is it a dead battery after 14 months of use?
G15 5511 Battery issue