Nine of Cups has two battery banks: a single 8D starter battery, and a four battery, 800 amp-hour bank that supplies power to the ‘house’ – our electronics, lights, pumps, refrigerator/freezer, water desalinator, autopilot, etc. – pretty much everything electrical except the starter. If we are anchored somewhere and are running the refrigerator and using our computers, our solar panels and wind generator usually won’t quite keep up with our daily electrical consumption. Depending on how sunny and/or windy it is, the fully charged house battery bank will typically last 2-4 days, at which time we have to start the engine and recharge the batteries. Batteries can only be recharged a finite number of times before they start losing their capacity, however. The number of recharge cycles depends on several factors. Battery chemistry, depth of discharge before recharging, battery maintenance and battery design are the primary factors that determine a battery’s useful life aboard a cruising boat.
We last bought house batteries for Nine of Cups in Pape’ete, Tahiti, about 8 years ago. At the time, we felt Lifeline AGM batteries were the best option available, and we had them shipped from Florida to Pape’ete. We took care to treat them well, and they lasted considerably beyond their expected life of 3-4 years. For example, we never let them discharge beyond 50% of full charge, and we equalized them at the first sign of sulfation.
But, alas, even our high quality, well maintained Lifeline batteries aren’t recharging well anymore, and no longer respond to equalizing. I plan to do a capacity test on the batteries when we return to Cups to see just how much life is left, but it’s fairly obvious that they are reaching the end of their useful lives.
Replacing our house batteries is not like replacing a car battery. First, it is a major cash outlay. The least expensive price I found online to replace our four Lifeline 4DL batteries will cost us more than $2200! Then we have the difficult task of wrestling four 124 lb (56 kg) batteries out of the boat, and reversing the process with the new ones.
There is also the question of whether the Lifeline batteries are still the best choice for us. We were quite pleased with the current batteries, but a lot has happened in battery technology over the last eight years. Has one of the newer technologies - PTTL, Li-Ion, etc. – matured enough to be better suited to our needs? Is it now more cost effective to go with a different battery type? What new products are available? Would we be further ahead to buy less expensive batteries with shorter lives?
Before we plunk out a couple grand or more on new batteries, I need to do some research to make sure we make the best decision. I plan to spend the next week or two evaluating options, checking specs and doing price comparisons. If you are interested in batteries, you are more than welcome to come along. And if you know more about batteries than I do (which isn’t setting the bar real high), I welcome your input and comments.