I paid Apple ~$80 to replace my Series 5 battery… they actually just exchange it with another device. I thought it was worth it and happy to keep using it until I can no longer get the latest watchOS.
Interestingly, if Apple loses its patent case it won't be able to do this with the affected devices (if they are out of warranty). I don't know why there's a difference based on warranty status, but according to the legal blogs I read there is.