Tpfanco is a free and open source fan control software for IBM/Lenovo ThinkPads running GNU/Linux. It consists of a fan control daemon and a GUI to monitor tempertature sensor values and set thresholds. For selected ThinkPad models user-generated fan profiles are available.

Use:
$ sudo module-assistant a-i tp-smapi

and set in /etc/sysfs.conf:
devices/platform/smapi/BAT0/start_charge_thresh = 40
devices/platform/smapi/BAT0/stop_charge_thresh = 85

The tp_smapi kernel module exposes some features of the ThinkPad hardware/firmware via a sysfs interface. Currently, the main implemented functionality is control of battery charging and extended battery status.