Based purely on conversations with other full time cruisers, I believe that we treat our batteries within a fairly normal range – if there can be such a thing as “average battery use for a full time cruiser in the South Pacific” I think we fit the bill. That is to say, like most cruisers, we treat our batteries in ways they were not designed to be treated. Our batteries don’t die on us, we beat them to death.
Estrellita’s battery bank cycles mostly between 70 and 90 percent of capacity. We rarely discharge to 50% but we rarely bring our batteries to 100%. AGMs like to be charged to 100% regularly. This was just not practical for us for the most part. Running the Honda until our battery bank is 100% charged (or nearly) happened only occasionally and we haven’t plugged into shore power for two years. Our haul out facilities (when they had power at all) had different voltages than we use and no converters. We could add more solar or add wind but for various reasons (real estate mostly) we haven’t made that decision yet. Our solar does a good job and our regular use of our Honda EU2000 generator brings things up whenever we make water (details on the system here).
Our Sears Diehard Platinum Marine batteries (made by Odyssey) lasted 4 years before they stopped holding useful voltages at moderate levels of discharge.
That is…OK…not bad even.
It’s not terrible. Nothing to complain about, but nothing to get excited about. 600 Amp hours of batteries retailed for $1500 at the time we purchased (we had a coupon to knock that down a bit). That puts the cost at $375/year of service at full price.
Note: The customer service at Odyssey was delightful. Email responses from knowledgeable tech people that were detailed, fast and on target, even though we had purchased our batteries from Sears with the Sears brand. Sears basically wanted us to bring the batteries in. If you live/boat in the US, that would be actually very useful.