La Crosse Technology WS-9031U Instruction Manual page 11

If the batteries are used as the main power source:
1. Projected image brightness, alarm volume and back-light strength will
be weaker when batteries are low
2. Battery life time will be much less than 1 year; depending on the
frequency of projection and alarm.
TO USE THE PROJECTOR POWER ADAPTER
The unit comes with an AC-DC adapter for using the projector for an extended
period of time, such as throughout the night.
To connect the AC-DC adapter:
Important!
Make sure that your household voltage is 120V! Otherwise it can result in
damaging your Weather Projection Station.