[ltp] Force laptop to run from battery while plugged in?

[linux-thinkpad@linux-thinkpad.org]

Does anyone know, under Linux, how to force the laptop to run from
the battery, even while it's plugged into the AC outlet? Or, does
anyone know of any software that does the same?

Windows or the IBM power management software had a program that
would "excercise" the battery, i.e. deliberately run from the
battery while plugged-in, and keep the charge levels within some
range (never fully drained, never fully charged). This is supposed
to extend the life of the battery.

I'd like to do the same in Linux. I'd also like to do some power
consumption testing remotely (so the laptop needs to stay plugged
in).

Thanks!
Matt