This week SetSail asked our cruising contributors about their batteries. What type do you use (manufacturer and design)? How many amp hours? How often do you charge and at what voltage? What kind of voltage regulator do you use? How old are the batteries? How many cycles do you expect before they die? To what level do you normally allow them to drop before charging?

Wow…a lot of questions…

We’ve used all sorts of batteries over the years. Generally the results have varied-and been highly dependent on the care we took, or lack thereof. When we started to get scientific about the issues 15 years ago, we came to the conclusion that “traction” batteries, the type made for forklift operation (amongst other things) offered the best overall performance (charge acceptance, percentage of discharge vs. life, weight/bulk vs. usable capacity).

Traction batteries are available in many shapes and capacities. To find what will fit in your boat, and what they cost, look for a local industrial forklift battery supplier.

On SUNDEER, and BEOWULF, we used Trojan batteries. Ours have a rated capacity of 1500 80% discharges. We rarely discharge fully-unless we are equalizing-so the actual life cycle is probably twice this (or more). In the real world, the batteries will probably outlast the two of us.

We have 1000 amp hours of capacity at 24volts-800 of which is usable. This very large bank is charged by two Electrodyne alternators-which are rated at 140 amps at 29V, but which actually put out more like 120 amps each-which is plenty. These have remote diodes, with their own fan, so the alternators stay reasonably cool.

Charging is with a single step regulator. Nothing fancy-just very heavy duty. It is easy to change the voltage with a face mounted screw head. One regulator is used to charge both alternators. We normally charge at 29.5 volts on the hook. We drop this to 28.5 if we are powering for long periods. Once every eight weeks or so we do a full discharge, and then re charge the batteries-finishing with an equalizing charge at 31.5-32 volts.

How often we charge depends on computers. If we are doing a lot of work, we charge every day for about 45 minutes. If the computers are quiet, on the hook, charging is more likely to occur on alternate days-usually 45 minutes or so. However, of we know we have a motorboat ride in the offing, we’ll hold off on charging (we can go four or five days and still have reserve).

When we are at sea, under sail, power consumption really goes up. The norm is to charge once a day, usually for an hour and a half.