On our trip south we've discovered a few items that we will need to deal with. One of them is the house battery bank. It seems that our house bank isn't holding much of a charge anymore. So begins my deeper education in marine batteries and complex charging systems (if I do any upgrades, I want them to be compatible with the eventual addition of solar). Things I wanted to learn about anyway...but learning under the gun of a needed repair is not as fun.
I'm somewhat familiar with variants of lead-acid batteries and multi-stage chargers from my previous stewardship of an airplane. In the airplane case, the batteries are small due to weight concerns and expensive (because they are a certified airplane part) and yet need power to crank the engine and run electronics for a while if an alternator failure occurs in flight. So, squeaking out as much life from them as possible was always a goal, and 3~5 years was considered a good lifetime for those batteries. But marine is a bit different environment. Much larger batteries wired into banks. The need to run things like refrigerators, lights, and equipment without a charging source for days on end (deep cycling) is a bit different than running a few airplane instruments.
I started my investigation with the obvious...take a look at the house battery bank. I try to take a peek at all the boat systems periodically, but the house bank sits at the bottom of a locker in the cockpit and isn't the easiest to access. Add in the fact they are AGM VRLA batteries (what was once touted as maintenance-free batteries) and they were a bit out of sight - out of mind. Well, when i dug all the stuff out of the locker and removed the access panels to the batteries, I could tell that the batteries were not in good shape. Each of the 3 group 4D (20 inch x 9 inch x 10 inch or so) batteries showed minor signs of swelling. The two usual causes of this are heat related: Either a sudden rapid discharge (short) or overcharging of the batteries. Since I haven't experienced any shorts, my immediate assumption was that it was the result of overcharging.
|The West Marine Battery that makes up our current house bank.|
A year or so ago I had one alternator's voltage regulator fail and it was overcharging...but that problem was identified rather quickly and resolved. Since the boat is configured so the engines charge their start batteries and then any leftover energy is used to charge the house bank, I would expect the start battery to have failed first. Since it was OK, I doubt it was the culprit. The original charging system for the boat works in a similar manner, charging the start batteries and then letting power "overflow" from there to charge the house bank. That left only one culprit - the Xantrex inverter/charger.
The inverter is wired to the main house bank, and it includes a smarter multi-stage charger that is supposed to do a better job of charging and maintaining batteries. As a result, the charger needs to be set up with parameters for the type and size of the battery bank. I guess I shouldn't have trusted how the thing had been set up when we bought the boat. I found the parameters were set for a 3000Ah bank of wet cell batteries. Since the actual bank is only 600Ah of AGM batteries, this is probably the cause.
Of course, this means we need to replace the main house bank. The batteries currently on the boat are from West Marine and when I checked were about $700 each. Ouch. Looking around, I found similar 4D AGM batteries for a little over $400 each. Continuing my research, I found that many of these batteries aren't true deep cycle batteries and, as a result, likely won't last as long as other options. Reading a number of articles on marine batteries and deep cycling batteries, it seems that some of the best bang for the buck are golf cart batteries. It sounds like they are better designed for deep discharges than the big batteries. They also seem to have higher amp-hour ratings for a given size than the ones I have now. The down side is that each battery is smaller and is only 6 volts, so I would need two batteries connected in series to equal one of the batteries I have now.
|Trojan T-105 225Ah, 6v battery option.|
|US Battery 2200 232Ah, 6v battery option.|
Two group size GC2 batteries sitting next to one another are the same length, slightly taller, and just a bit narrower in width than a 4D group size so they should fit my battery locker. Wired in series, I would have a 12 volt equivalent with between 210 and 225 Ah (compared to the existing batteries at 198Ah). The wet cell batteries seem to be around $110 each (or $220 for the equivalent to one of the 4d's), and the AGM versions are around $200 each (about the same as the cheaper 4D's that I've found). Since these produce a slightly higher amp-hour bank that is more accepting of deeper discharges (to 50%), this may be the way to go. It would require I get 3 new cables to wire two 6-volt batteries in series, but it seems to me the advantages may be worth the limitations.
|Trojan AGM 217Ah, 6v battery.|
|US Battery AGM 213Ah, 6v battery.|
Decisions, decisions...if anyone has any advice, leave a comment.