With it failing when you crank the motor, that could indicate low voltage to the unit. Low voltage is a killer for electronics. If your unit is wired to a power source under the dash on a circuit board of some thing like it, I highly recommend changing the power source. I would run power wires directly to the battery with an inline fuse. Your unit is under warranty now, but if you continue to use a power source that doesn't provide proper voltage, you might have failures later when it will cost you! I'd also take your battery to an auto parts store who can load test it for you. It might read 12v with no load on it, but drop considerably under a load like when cranking the big motor. Electronics are too expensive for guess work.