I don’t feel like focusing on fixing things at home is the best way to ensure device longevity.
Creating a demand for technicians that can replace all kinds of things on our phones makes it so there’s always some phone repair shop nearby. Every mall I frequent has one. This creates a lower threshold for keeping the phone alive no matter what goes wrong with it.
The battery on my last phone outlasted the phones useful lifespan, so it’s not like batteries on modern phones is a part that’s particularly likely to need replacement. Every user is different of course, some go through a lot more charge cycles. But then there’s others that often break their screens. Or their charge port. If all these things should be easily user replaceable without tools, the phone would become very bulky.
I feel like we’re pretty close to a good compromise, now that Apple has a program to do these kind of replacement at home if you want. It’s really not that difficult.
If you want - you can buy modular phones, pay for that, don't force other people
And I'll go and pay a couple dozen bucks for this work, like all normal people. But eco-activists are starting to say that eWaste is caused by non-replaceable batteries, not by the obsolescence of devices. No one will change the battery in an outdated device, even if it is replaceable.
There are pros and cons everywhere, so far I see more cons.