Using the Battery Pack
  Notice 
If the computer enters suspend mode because of a low
battery condition, the computer will go into hibernation
mode before the battery power is completely used up. This
capability is disabled as a factory default. You can enable
or disable it with Suspend/Resume Options from Power
Management in the ThinkPad Configuration program. If
the system goes into hibernation mode, replace the battery
with a fully charged one or supply the system with AC
power. Do not disconnect your system from AC power until
the battery is fully charged.
  Chapter 3. Using Battery Power 91