If it's frying the board....sounds like too much voltage, not a lack of it. Check that fuse and make sure it's not too high a rating for the unit, then figure out if you've got voltage surges. Also, make sure you don't have a wiring connection some where that's getting wet. Combined with a bad or overrated fuse, that could fry a board.

Course, with the separate battery and new direct wiring, you should be fine. Also, I'd think HB would tell if you're frying the board and would tell you on the returns.