Compaq 1610 Reference Manual page 40

If replacing with a rechargeable NiMH battery pack, follow
the steps in the illustration below. Be sure the flat side of
the battery is facing in toward the battery compartment as
indicated.
If using a rechargeable NiMH battery pack, connect the
6.
device to AC power and allow the battery pack to charge for
three hours. If using AA alkaline batteries, proceed to Step 7.
Turn over the handheld PC, raise the lid, and press the power
7.
button to resume operation.