Rock- Check the voltage output of the Hobbywing BEC, I bet it's low. I had a cell go bad on one of my lipo's, so when I plugged it in I was only getting 3.9 volts and my 4PKS rig was acting exactly like you describe. Or maybe you have a bad lipo? But if it is the BEC on the HW, you can bypass the BEC and run a rx batt (of the proper voltage) to be able to run your SC.