I wanted to add to what Easy said about normal variation of 0.7 to 0.9. Although these numbers aren't too out of whack, my boat has a natural voltage of around 0.87....which I found to be too high. Last summer fishing in Canada (before I had a BB) I had very few hits while trolling and most the people I talked with thought I was running hot. Now that I have a BB, I run it between 0.6 an 0.7 and have had far better success.