I use 1800Mah NiMh batteries in my transmitter, and a 5-cell 1000Mah NiCad reciever pack. I don't think they were fully charged at the last race meeting, but they lasted about 45 - 50 minutes of driving.
I think they could've gone at least 1 1/4 hours, when I got home I switched the Tx and Rx on to discharge them and it took about 5 - 8 hours for the Rx pack to die! I know it'd die quicker if I was driving the car, but now I don't have to worry about how long they'll last
I was worrying when I was using 4 old 600Mah NiCads for the reciever battery and 8 of the same in the transmitter.