Both the CPU and the receiver chip runs on 3,3V and the voltage regulator IC needs 3,4V at ambient temperature to keep its output at 3,3V. If it gets hot it needs a higher input voltage and can't supply as much output current. If it drops its 3,3V output it might make the scanner work unreliable. Having 3,85V from battery should be okay but it's probably something wrong with that regulator IC and then needs a higher voltage.
Setting the battery low warning to 3,4V will warn you that the scanner might not work properly and setting it to 3,7V will warn you that you probably have one hour left of normal operation.
/Ubbe