This is old but for anyone reading, you can definitely power all current Apple TV motherboards with various power supplies. As long as you confirm you are using a properly rated one it will work though if it is out of its housing you lose the heat sinks/fan. (Running Apple TV just fine from bench supply)
You’ll only be able to buy replacement boards on eBay or similar. I have successfully repaired a number of Apple TV 4K that had no power issues by fixing various shorted components.
You won’t be able to source the original battery as it is spot welded to the lightning port cable and mobo cable, and is one unit. However if you can solder I have successfully replaced two remote batteries for about $6-$8 a battery.