Check what the insurance policy covers you for. You need consequential loss to cover any claims against you. The product warranty will cover replacement should the product fail within the warranty period. Find out which disclaimers you can use and are legally binding. In the end, any product can fail either in warranty or out of warranty, there is nothing that you can do to prevent that. Can you design into the system that the product fails safe, i.e. overvoltage condition is monitored and displayed using independent system and the instruction states that the owner/driver must pull over and stop the engine at the earliest opportunity as the battery will no longer be charged. What happens when your car displays 'engine fault' ?