Here's the guide:
Battery calibration The Solution:
- You must drain your battery all the way to 0%, or as close as possible.
- To do this simply play a game, video, etc until the steam deck shuts off (not a random false shutdown as above, but a true low battery state). Your deck may go into battery storage mode in which case the power LED will blink three times and you will not be able to turn it on without plugging in the charger. If your deck goes into this mode, plug it in to perform the next step.
- Then hold the volume up button while pressing the power button. This will boot into the BIOS settings menu. The goal here is to leave the deck on this screen, which will not automatically dim, to drain the remainder of the battery. Leave the deck on this screen until it dies on its own.
- Now here is where we are going to deviate a bit from the steam support advice. Perform this BIOS drain 1-2 more times until the deck is so low on battery that it can no longer even make it all the way into the BIOS before dying. You may have to briefly plug the charger in to get it to restart. It seems that doing this step once may not be enough to fully drain the battery, which is the key to this entire process.
- From here there is one more crucial step to ensuring that the re-calibration is successful. The deck needs to remain off while charging overnight. If there is residual battery power left after the above steps, the deck may automatically power on and attempt to boot into SteamOS immediately upon plugging in the charger. If this happens you will need to unplug the charger, and as soon as the deck dies, plug it back in, so that it is completely dead and off while the charging process begins.
- Now let it charge overnight without touching it (at least 6-8 hours). In the morning it should still be off, and in my case even the power LED was not lit. Now try turning it on, entering desktop mode (by holding the power button), and checking the battery health in the taskbar. It should be over 90%. In my case battery health is now reading 100% from 12% prior, and now seems to be reading and functioning correctly. I will update if I continue to have any issues.