I miss the good ol days when my T410 just simply unclipped. Completely modular, no screwdriver required, almost like battery replacement was a feature!
For a while, up until the T480, you had both an external and the internal battery. So if you had a few batteries it was pretty trivial to swap them while on the go--and sometimes you really do need 18 hours of battery life on a laptop, even if you aren't pleased about it.