When I have my battery switches in the BOTH positions, one of my batteries gets very HOT. Too hot to touch!! When I move the switches to the 1 position the battery cools down.

When the battery gets hot the boat is not running and there is nothing electrical turned on. Anyone knows what is going on?

disconnect the neg and pos from the batt that gets hot check voltage at the terms with a vom and see if your terms are crossed sounds like something connected to the hot batt is rev polarity.. possibly the merc cathode>if equipt

Wow!. Only 1 reply?

Here's my guess: The battery that is getting hot has a cell shorted. When the battery switch is in "both" the good battery is trying to charge the (low voltage) battery with the shorted cell...heating up the bad battery.

I'd guess when the altenator is charging the bad battery the same things happens....maybe less heat than when switch is in "both"...but it still gets warms.

I suspect if you replace the battery that gets hot, the problem will be fixed.

Let me know how this turns out.

Was surprised to see limited resoponse to this question also. I have not been able to check the problem out do to bad weather. Looks like today may be the day.

I might add that this, problem happens when the boat is not running and no power draw at all on the batteries;

I agree with beakboater, if that is the problem doesn't matter if the boat is running or not, it is the dead cell that is the current draw.

Have you changed anything lately that may be caused the wiring to get switched?

I have not changed anything YET!!!. Boat is new to me. I just purchased the boat from Shogren's and ran across this situation.

My guess is it is the battery also. I'm assuming that the batteries are originals and 1 has gone bad. Batteries are Northstar's. Don't know much about Northstar's. Just want to make sure I find the right problem before I start changing 75lbs. batteries in and out of the enging compartment.

Assumming I'm right...wich doesn't happen often! When the battery switch is on "both", the good battery is charging/heating up the bad battery. If the battery switches are set to isolate the 2 batteries, and the boat is running, then the alternator would charge/heat up the bad battery, but perhaps not as much as when switched to "both". Reason being, a good battery can supply much higher current than the alternator...for a while!



I might add that this, problem happens when the boat is not running and no power draw at all on the batteries;[/QUOTE]