That sounds a bit weird. Perhaps the unit is malfunctioning?? Too bad could did not measure the voltage while cranking.
I like the 235A but if the voltage is out of control and ruins electronics on boat would it not do the same for a car?
I've had no experience with those things but something does not sound right.
-Karl
1986, 32' Sedan, twin 360ci, 275hp Chrysler's w/ K&N flame arrestors