The funny thing is that cellphones have gotten slim to the point that adding replaceable batteries and upgradable RAM wouldn't make them ridiculously thick or heavy.
I don't believe a replaceable battery needs to make a phone any thicker or heavier. Just take anything that's glued now and secure it with machine screws instead. "Replaceable battery" isn't the same as "swappable in the field with no tools", and while that's nice to have, it's not necessary in order to forestall device obsolescence.