[Al Skierkiewicz]

Aaron,
Backfeeding relays should cause no appreciable harm to the relay unless it is done repeatedly and without circuit protection. However, the Spike, Victor and Jaguars have no reverse polarity protection if you connect battery to the output. As I remember the Spike outputs are both shorted to the negative lead of the battery input connector when it is not powered, so the breaker feeding that branch should trip right away in that condition. I think you meant to say that the fuse on the Spike is a fast acting fuse but again it is in the positive power side of the Spike in series with the relays. This fuse may not trip if the Spike is wired improperly.