The relief in the boat when we finally ordered our batteries was palpable. This has been the decision that would not go away. It was easier to choose our boat -- love at first sight -- than choosing a replacement battery bank.
Our current battery bank is 150A of Interstate Gel batteries plus a start battery. Our experience suggests these would make a good choice for a weekend warrior at least if not more. With mostly shore power, a lot of weekends, and a few longer trips, they've performed consistently and maintenance-free for the past 3 years and I'm not sure how much older they are because they came with the boat.
In my opinion, "consistent and maintenance free" must be the highest praise a piece of boating gear can receive.
We looked into every type of battery and at various moments have been "ready to buy" golf cart batteries and "ready to buy" Odyssey PC-1800s.
The Sears Diehard Platinum Group 31-M Batteries are made by Odyssey and are the same batteries inside a different case. I called Odyssey myself and they verified both of those statements.
Everyone has strong opinions about batteries and I believe that is in large part because of differences in how they use them, how they charge them, their budget and their tolerance of battery maintenance. Some people want the cheapest batteries per cycle over the long term. Although cost matters to us, we put a premium on our free time as well. There is enough maintenance on a boat to keep us busy as it is.
I want to put my batteries in their hole, with a strap down, and forget about them except for charging them to 100% once a week. I also want to minimize the amount of time I have to run my generator to get them topped off by having them accept charge like a thirsty camel and also to have a big enough battery bank and enough solar that we can go days between running the generator. Beyond that, I want them to work, and to keep working for a long time, until they don't and then I buy new ones.
Enter the Odyssey/Sears, the better thirsty camel of the battery herd.
The big flashy news about Odyssey's is that they can accept a larger amount of charge at once than other AGMs but this fact wasn't particularly valuable for us because, at maximum, we will only ever be able to generate 80-100Amps incoming. What was very interesting to us is that they can take a higher rate of charge all of the way to 100%. All batteries, including Odysseys, taper off in their charge acceptance rate as they reach full, but Odysseys flatten out less than others.
This fact is exciting because it means decreasing the amount of time we have to run the generator when we do run it and increasing the likelihood that we will be good battery owners and charge them to 100% regularly which AGMs need for their longevity.
With the purchase, our battery bank will increase from 150AH to 500AH. For the non-boaters, actually I am certain that no non-boaters will have made it this far in the post, you use your batteries down to 50% (ish) and then need to charge them so you don't damage them.
At 150AH we have to charge them every day at our current use of about 75AH a day and our amp usage will go up as we start cruising full time meaning we would have to charge them twice a day with this wee battery bank. At 500AH we would have to run the generator every 3rd day if using 75A and that is assuming NO solar input.
We are planning to install the batteries when they arrive in 2-3 weeks and we'll talk about the installation then.