First suggestion - RMA it
Second suggestion, if you wanna try to fix it yourself either in the meantime or before RMA:
- Play games on it until it completely runs out of charge
- Launch into the bios until it completely runs out of charge
- Repeat the above until it no longer turns on
- Plug in your Steam Deck. If it turns on automatically, repeat the above two steps until it doesn’t when you plug it in
- Leave it charging and turned off for 6-8 hours, preferably overnight, then turn it on and check again
If you’re back up to 95%+ then it’s a battery calibration problem which most are
The equivalent of about $350 for a 256GB to a friend. My RMA replacement had just arrived so I sold it brand new