Well, I tried disabling the low voltage cutoff and also moving the reciever to a different part of the model in case its positioning was causing interference. Same result
The battery last for ages...like 20 minutes and it was still going strong, so I think its in good nick. Its brand new anyway. I was wondering if maybe the problem is with the radio. Another problem I found was sometimes, when I push reverse, the car lunges into full forward throttle. Its so unpredictable as to be to dangerous to drive near other peoples property. It randomly crashed into my neighbours car earlier! (no damage fortunately).

I have some old model aircraft, could I take one of the servos out of one of them and try that to see if that changes anything? Are the servos all a standard size?