Should we get 4 or 6 GC2 Batteries?

[redpointist]

I'm starting work on the electrical system for our 34' sailboat that the two of us will be living aboard and cruising full time. The boat had 2 six year old 12v batteries that had been abused, so they're getting thrown out. I'm wanting to replace them with 6v GC2 batteries, but I'm not sure how many I want to get.

We will have about 500w solar, and don't currently have refrigeration, but I think we'll be installing it. We won't have air conditioning or hot water heaters though. We have LED lights so that helps, but I do like to run the laptop a lot so that hurts...I know the question is best answered by adding up our daily electrical load, but having not lived onboard yet, it's hard to say exactly what our usage patterns will be.

I feel like 430AH (4 batteries) will be tight with refrigeration, and maybe we should go ahead and spring for 645 AH (6 batteries). I also like the idea of having some excess capacity so we wouldn't necessarily have to run the motor to charge after 1 cloudy day. I would get 4 and then get 2 more later if needed, but it seems to be a no no to mix batteries of different ages.

Is 645 AH in 6 GC2 batteries overkill for a 34 foot monohull? Theres plenty of space right now, but once we start packing the boat full of our stuff I wonder if I'll regret having the extra 2 batteries?

[onestepcsy37]

Because of the large amount of solar you have I think four would be plenty. You may get as much as 150AH a day from your 500W panels, which should really keep your batteries topped up. Without refrigeration you seem to have a very light load, so four is probably more than enough. If you install a fridge you will probably still be ok.

[S/V Illusion]

While cruising,battery capacity is more important than money and I never met anyone who complained about too much of either.

From another perspective, the less you draw them down, the longer their useful life and obviously, a larger bank equates to higher minimums.