Almost all my inside phone batteries I’ve had in cheaper knockoff phones have been replaceable. It’s not as easy as pulling the back cover off and instantly swapping it, but it’s not THAT much harder. It’s doesn’t exactly require microsoldering. Which is the reason why I know my last three have been replaceable despite being in-house.
Manufacturers really just need to make better and more secure charge ports. Having to resolder my last two blu phones and a Samsung because the charge ports go bad is just annoying.
Never had issues with a battery in all my years of using smartphones though.