Q-See QSDB8209C - Manual (Page 8)

Note:
--This receiver can also use dry batteries as a power source by loading 4 AA
batteries into the battery compartment at the back of the camera with their
polarities in the correct position.
--The AC adapter will work instead of batteries after it is plugged in. If the
camera is not going to be used for a long period of time, please unplug the
adapter and remove the batteries.
* The camera can run off of batteries for up to 5 hours.
2. Adjust the volume control to the desired level.