Well you still have to go through the manufacturer and/or you need special tools, you’ll also get “genuine battery” warnings even with an original battery if you go third party or DIY. Ideally it should be thought through to be accessible for users to do themselves. And as you say, batteries aren’t the only or biggest offender.
For power efficiency, you get the added benefit of being able to run on battery backups for longer. This for pihole, file servers, etc. can be a lifesaver