I have a brand new battery. I am not running into any problems so far I just was testing to make sure everything was fine before taking the boat out on the water. When I measure volts across my battery with the engine running I get 12.21 volts. But if I go to the alternator and measure from grnd to the only positive terminal coming off the alternator I get like 10.5. that wire goes to some kind of amp looking device with about 5 bolt down wire fasteners on it. the lead to the battery comes off of that amp and so does a wire going to something that looks like a solenoid mounted to the engine block. if I disconnect the lead going to the battery from the amp the terminal on the amp reads the same as the alternator output I am getting. have let the boat run for up to an hour with no problems. However at that time I was not worried about this and did not measure voltage. I am not sure if this should work on a boat like I think it does on a car but i unhooked the negative cable from my battery and the engine died. I thought if the alternator was working it would keep running. Should I unhook the alternator lead and measure current? or should I take the alternator to autozone and have it tested? I looked up re[placement alternators in a mag I have and the cheapest was $500, is this true of all marine alternators>? Thank You in a Advance. Sorry for the long post