Compaq 1610 Reference Manual page 35

The C-Series displays various battery icons in the status area of
the taskbar when batteries are low. When you see a low or very
low battery icon, save your work, turn off the device, and replace
the old batteries with fresh ones as soon as possible.
If no action is taken to resolve the low battery condition described
above, a critical low battery warning will appear on the screen
when the batteries enter a very low state. When you see this
warning, take immediate action by saving your data, then do one
of the following:
Turn off your handheld PC and replace the batteries.
Connect the AC Adapter to your handheld PC until new
batteries are available.
When the main batteries are too low to run the device, a final
warning message appears notifying you that your handheld PC
can no longer run and will be shut off. This is followed by an
automatic shutdown which saves all data and suspends operation
until new batteries are installed or until the device is connected to
external power.