seanlong.orgposted on: January 20, 2014
The "Out of the box" battery performance in FreeBSD is a little lacking. The following changes almost doubled the battery life on my Lenovo T420 (integrated Intel graphics version).
in /boot/loader.conf add
drm.i915.enable_rc6=7
hint.p4tcc.0.disabled=1
hint.acpi_throttle.0.disabled=1
in /etc/rc.conf add
powerd_enable="YES"
performance_cx_lowest="C2"
economy_cx_lowest="C2"
I recommend using the acpiconf -i 0 command with the laptop running on battery before and after these changes to see the results. Monitor the returned Present voltage: value.
I did not dream up these changes, just experimented with some values found at FreeBSD Wiki and FreeBSD Forums
