Compaq 1610 Reference Manual page 41

A CR2032 lithium coin backup battery (available through your
local reseller) comes preinstalled in the handheld PC. Be sure to
replace the backup battery as soon as possible when it shows
signs of low power (such as when the low battery icon appears in
the status area of the taskbar).
!
To replace the backup battery, follow these steps:
1. Save your work.
2. Turn off the handheld PC by pressing the power button.
3. Close the handheld PC and turn it over.
4. Loosen the screw on the backup battery compartment cover
using a small Phillips head screwdriver.