FC5 laptop powers down despite full battery

I have installed Fedora Core 5 on a Sony Vaio PCG-Z505LS laptop. I have done my "yum update", and also installed the suspend2 kernel available from mhensler.de. And my laptop is running in apm mode. I use KDE, Gnome is not installed.

Linux localhost.localdomain 2.6.17-1.21571.rhfc5.cubbisuspend2 #1 Tue Jul 18 12:10:45 CEST 2006 i686 i686 i386 GNU-Linux

When running on the battery, I have the problem that the laptop suddenly powers down, as if "shutdown -h now" had been issued. I think I have glanced a message on the screen about low battery power just before it happened, but I'm not positive -- the screen is quickly taken over by the stream of "shutting down this and that OK" messages. When I start the laptop right afterwards (without any charging), the battery is almost full (80-90% in the cases this has happened).

The apm command gives a reliable percentage number for the battery, but gives rather random amounts of time remaining, ranging from a few minutes to several weeks when the battery is almost full.

Off-line, battery status high: 96% (20d+14:56:00) Off-line, battery status high: 96% (0:21:21)

So my question is: how can I prevent my laptop from shutting down at random? Completely disabling the ability to shut down on low battery power would be an ok option.

"System beep" and "Notify" are selected under "Low Battery Warning-Critical".

Thanks for any help in advance! Anders