You should try ZFS (not on the SD, though). It’s pretty solid and used in NAS very often.

Yeah, Linus Torvalds has been pushing for ECC RAM everywhere for just this reason.

The real risk is losing a bit of time with this. Since everything is backed up anyways, the data is just a restore away.

If you don’t have a backup, that’s the risk and has nothing to do with this procedure.

For the Steamdeck the risk is even less, since Steam backs up savegames automatically and the games can be re-downloaded at any point for free (except for Unity developers, who have to pay 20 cents for this).

Any good battery management system should avoid that.

When the SD is discharged, it tries to charge from the external power source (it doesn’t know that it’s a battery and not a charger). Battery to battery charging is just losing energy to heat. So, it’s probably better to discharge the external pack while the SD is at 100%.