Power and 802.11b PC card usage

Last week was a wonderful field test for my iPaq/PC card
sleeve/WaveLAN Gold card. For the entire week, I used this plus my
Stowaway keyboard in lieu of my notebook during the Black Hat and
DefCon conferences. Almost everyone who saw it was impressed. Doubly
so when I explained it was running Linux and X11.

One oddity I noticed: Once the battery reached the neighborhood of 50%
charge (as reported by apm; this generally took 2-3 hours of constant
wireless/keyboard use), the 802.11 card would cease to function. In
fact, the card would lose power, and the OS would no longer report a
card present in the slot.

Have other people experienced this? Is it a known problem?

-- 
Mark C. Langston
mark_at_bitshift.org
Systems & Network Admin
http://www.bitshift.org