Juniper Field PC Owner's Manual page 8

3. Push the battery door closed until the slide latches click
into place. If the latches are not securely in place the unit is
no longer water tight.
Note: Do not turn on the Field PC yet.
4. Plug the AC wall charger that came with the Field PC into
the wall socket.
5. Remove the rubber protector from the Field PC's external
power input jack.

Field PC Owner's Manual