It IS a good idea. My step mom had a high end Samsung phone (not sure exactly which one) and it’s battery degraded enough within a year that it began to shut down randomly a lot.
They're replaceable, but they are clearly not meant to be done by the user. There were many opportunities to break pieces of the phone or ruin it completely. It's a horrible design.
But it was a hell of a lot cheaper than the quote I got from the repair shop, and I didn't break anything. (Which isn't a surprise... I like fixing things.)