BrianG,
I tried 5 cells when I got my DX3R a while back with old 2000 mah AAs I had. The 6.4 volts they pumped into the radio freaked me out a bit so I went back to 4 cells. How long have you been running with 5 cells? I'd like to go back to 5 cells if I was sure nothing bad would happen to the radio.
