salnsp

Hard to tell exactly what's going on as you do not know what controller you have. That's unfortunate. My first guess is that you are experiencing a shut down due to low voltage cutoff. I might think that the speed control is set for hard cutoff. Li-Polys do not like a hard cutooff as they can sag a bit when throttle is advancing. This causes the cutoff. It also may be due to the battery itself. If the battery is old, or just cannot keep up with the demands of the motor and speed control, you will go into cutoff.

I would try to find the information on the esc and try to program it for soft cutoff. If you can do this, it should take care of the problem. Make sure you have a good name brand battery to work with. If you cannot find info on the controller as a last resort replacing it would be an option.