TAG MIL-BOOK 10 - Manual (Page 45)

If you do not take any action and after two minutes’ of warning beeps, the
computer will automatically suspend-to-disk and turn off.
CAUTION:
If the “Battery Low Warning Beep” item is disabled in the Setup Configuration Utility
(SCU) program, the computer will not beep.
If you are using a flash PC Card, do not access the card during battery low periods.
This is because the access may take longer than the time it takes the battery to run
out of charge, thus making your access to the card unsuccessful.
If you fail to save your data when the battery completely runs out of charge, then
you lose your data.
Managing Power 3-7