ORIGINAL: Tired Old Man
Here's a real simple answer. If you have a 4.8v battery a very safe place to stop using it will be at 4.8v. That will work every time. Why people seem to think they should take batteries below nominal voltage is beyond me.
Some Transmitters will warn when the voltage gets below 8.8 volts. That is 1.1 volt per cell for a 8 cell pac. Seems like 4.4 would be absolute low voltage discharge...but safe.