An old HP laptop with Debian hosting Klipper and Home Assistant. Waiting for an OTG cable so I could replace the laptop with a phone for less power and heat
On a related note, I solved the battery issue with my wall mounted Fire tablet (for an HA dashboard) by connecting the power supply to a smart plug and setting up an automation to only give it the juice for about 3 hours per day, spread throughout the day
I've done similar with an old Android tablet. Installed Fully Kiosk Browser to display the dashboard AND read the battery level - above 75%, switch off power...
But... automations only trigger when going past the threshold once, so if there's a random issue where HA doesn't see the battery drop below 10%, (had that happen a few times in the past), then I also have multiple triggers for 5% and 2%... to turn the power back on again 😉
Yeah, the tablet runs Fully Kiosk and I tried the same thing with the battery percentage thing and ran into the same issue, so I just simplified and made the automation time-based.
The tablet also likes to freeze a few times a day, so I also created an automation that toggles the smart plug power whenever HA loses connection to the tablet for more than 5 seconds, then toggles back to the original state at the start of the automation, which corrects the problem. Until the next time. But hey! It was only $60, so it's fine.