Here is a chart that shows what the Macintosh Portable is doing at various
battery charge levels:
Battery Voltage Macintosh Portable Status
--------------- ------------------------------------------
7.2 Charging with adapter
6.4 - 6.0 Battery without adapter (normal operation)
5.9 1st software warning
5.86 2nd software warning
5.8 3rd software warning
5.76 10 second warning
5.72 Software shutdown
5.65 Hardware shutdown
5.4 Battery sulfation
Once the Macintosh Portable's battery reaches a voltage level 5.72 volts,
the machine goes into software shutdown mode. This will occur regardless
of the activity of the machine, even when connected to AppleTalk networks.
This mode is equivalent to sleep mode except that the Macintosh Portable
will not come out of software shutdown mode until the battery charger is
plugged in or a battery with more than 5.8 volts is installed. Once in
software shutdown mode, the Macintosh Portable will keep the contents of
memory intact for about five days.
When the Macintosh Portable's battery reaches a voltage level 5.65 volts,
the machine goes into hardware shutdown mode. This mode removes power
from the entire system except for the Power Manager chip. All memory
contents are lost. The Macintosh Portable will not come out of hardware
shutdown mode until the battery charger is plugged in or a battery with
more than 5.8 volts is installed.