Roy - I looked at the same 7650 Blue Sea Add-A-Battery kit and called them on it. It's only rated to 120A. My concern was that my alternator puts out 130A and I will probably go a little larger alternator when this one eventually fails.
I called them see if the extra 10A was of concern. I was hoping when they rated it at 120A the relay wouldn't be hurt by the extra amperage but would just ignore it as unusable. The tech person said not to use the 7650, but go to either the 7620 or 7622 rated at 500A continuous.
So check your alternator and think about if you'll go to larger one in the future.
Bill
