Batteries are critical. I have had units that someone thought they could put any budget battery in there create constant issues. The drive has a board called the CANIVF which is a royal pain. It is what talks to the rest of the system. Schindler doesn't sell it. They will repair your drive for a price worthy of grabbing your ankles. If the unit boots after pulling the VF plug, chances are this is your issue. But...bad batteries will cause the SEMNA board to constantly trip. So make sure the batteries in the TSU (mounted box in hatch adj to top floor) are good and of the same Amphours rating.