With other laptops, I've noticed that after a year or two of use, they become nearly useless on battery.
AIUI this feature is built into lithium chemistries. If you don't like it, buy (heavy!) batteries using a different chemistry.
I was talking about maintaining a battery which keeps its ability to hold a full charge. ie. By only charging the battery to ~90%, you can discharge/recharge it many more times, and still get close to the original life out of it, rather than if you charged it to 100% every time.
If that's based on what "some bloke in the pub told me", I strongly counsel you to check if it applies to the chemistry you're using. This is not my field, but I know that best practices are not portable between e.g. NiMH and Li chemistries. * * * AIUI your original question was how to get the same functionality (stop charging at 90%) while under Linux. That will depend on vendor- or hardware-specific drivers for your thinkpad, possibly something like acpi-thinkpad.ko. And if it doesn't exist, then you can't have it (unless you keep a dual-boot Windows install around purely for the purpose of toggling between stop-at-90% and stop-at-100%). Sorry. I didn't mention that initially because I was hoping someone that actually owns a thinkpad would reply with more specific details. :-(