Ask PYS: Power

Grant, on May 30, 2011 asked:

I have twin inboards with a generator. The current set up (I believe) is a dedicated starting battery for each engine and one house. I am draining my house battery too quickly. What would be the optimum battery management system?

Hi Grant,

Having a dedicated battery for each engine might be overkill. It certainly provides the maximum amount of redundancy but I don't believe it is necessary. As a starting point, you could limit yourself to a single battery for each inboard and another battery for the genset.

Very few boats are actually designed for the extended cruising that attracts so many boaters to our local waters. I'm unsure what you mean by "quickly," but, in any event, it should last for at least 24 hours. You might need to consider getting more battery capacity for your house to at least give you 24 hours at anchor.

In terms of charging, you have three alternators on your boat. The genset alternator should stay dedicated to the generator battery, one of your inboard engines should charge the engine battery, and the other inboard should charge the house. If you want to go a little further and have faster charge rates, you could have your engine battery also be automatically combined with the house battery.