To the editor: I’ve just been reading Nigel Calder’s article titled Battery revolution (Issue #192, March/April 2011). For the particular application he is interested in, i.e. dockside or fossil fuel, recharging sources where high charging currents are available, high charge acceptance rate (CAR) batteries make lots of sense. However, they do not make sense to those of us who are long-distance cruisers trying to avoid visits both to marinas and to fuel docks. CAR is of no consequence if you are trying to build a green boat, since our charging sources are low-current output with long time spans. In a green world, efficiency is the holy grail, not CAR. The problem he failed to mention is that high-charge and discharge currents are the cause of the inefficiencies he describes. Reading the manufacturer’s literature, it is clear that at much lower currents, the charge and discharge efficiency of standard lead-acid technology is much higher. Furthermore, if you design your solar and wind energy sources to be greater than the daily load plus the losses, then you charge to 100 percent each day and do not suffer the shortened battery life of the 50-80 cycle regimen. No equalization is required. Thus less expensive traditional wet cells along with plenty of solar panels are still the way to go for the green cruiser.
—A former electrical engineer, an active pilot and a lifetime sailor, Charlie Freeman and his family live aboard their 1988 Tayana 37 cutter Kamaloha. They are currently in Curacao.
Nigel Calder responds: Other than catamarans, very few cruising boats have anywhere near sufficient solar and wind power to keep up with the house loads, and as a result most spend long hours running their engines at anchor to charge batteries (it is not unusual to run engines or generators two to three hours a day). High-charge rate batteries, especially when coupled to high-output alternators or, in the case of generators, powerful battery chargers, are particularly appropriate in this scenario as they substantially increase the average charge rate into the batteries with a concomitant reduction in engine run hours. In fact, when battery charging at anchor using an engine as the power source, the reduction in engine run hours is directly proportional to the increase in the average charge rate. Of course, if the boat has enough solar and wind to keep up with the house loads, then Charlie is correct.