Alan,
Running my Tamiya Tiger I Saturday afternoon to the point of "out of gas" stops movin, engine shuts down and starts back up. The battery pack that was on the drive set read 5.84 volts when I hooked it to charge. If about 6 volts is the cut off, it may be to low to protect lipo. I do run lithium in my KT and Panther but they last so long that I dont worry about discharging them below a safe point and I alway check the voltage befor and after running. Hop this helps, Paul