My Boat Works

5 Responses to “Some Quick Basics of Boat Batteries & Chargers”

1. Jerr Says:
   October 27th, 2009 at 10:34 pm

   I’ll write a detailed series of articles on this at some point but until then, here are some brief pointers you can discuss with your boat electrician to keep the work tidy and truly correct:
   * Bond everything metal (assuming a glass boat) to eventually a zinc, with clean connections. The majority of faults are on ground, rather than hot sides.
   * An isolation transformer just inside shore power will do your boat’s electrolysis wonders.
   * While AGMs are terrific for cranking amps, don’t leak or need filling, are vibration proof and can be mounted on edge, they are highly sensitive to low voltage and thus do not make good house batteries.
   * A good gel cell can be brought down very low 500 times without damage but can not deliver or receive high amps without damage, so they’re ideal house batteries but will die quickly as starters.
   * Gel and AGMs take different charging regimens, so the most efficient method is to have a separate charger for each. Obviously, this is not a good solution for budgets but it’s awesome and pays many times over, in the long run. I’m still running my two 8D gels for my house bank, installed in 1994.
   * A good 3 or even 5 stage charger isn’t expensive and really worth its weight in gold – Check out the capabilities and doublecheck with the wholesale battery salesperson (Make sure you’re talking to a senior person!).
   * Buy from a battery wholeseller and take time to ask questions about quality – There’s a ton of different purposes and you’ll find vast differences in amp-hours, life-cycles and cost. An AGM I commonly install is Trojan – They’re terrific value and come with a 5 year guarantee. Whatever you do, don’t buy “boat” batteries – They’re just marked-up and usually the cheapest in their class.
   * Proper busses work wonders – Think the system through and leave 50% capacity. You’ll probably use half of that and be glad for it.
   * I label every end, 8″ from the end, of every wire and match my busses + & – side by side, with labels in between, in the same order as the switch panel.
   * I also leave workman’s loops (loose) so I can later pull wire. I know I differ from tradition here but no one’s ever had a complaint and I’ve had lots of compliments when customers later run wires or replace equipment.
   I’d also check to see all ends are sealed in exposed areas and tell the boat electrician you’re going to look for proper sealed terminals everywhere. If you bring these points up, I’m sure you’ll be taken seriously.
   One last thing: Nigel Calder’s Boat Electrician’s Handbook is IT! Buy it and you’ll understand everything. It’s written very clearly and has great diagrams and pictures. Best wishes!

2. Gtod25 Says:
   November 4th, 2009 at 9:57 pm

   Jerr, outstanding stuff. Once I get the time I must ask a few more questions about your view on AGM’s as a house bank. My fear of Gels is their intolerance to overcharging.

   Thanks

   Gerry

3. jcluddite Says:
   November 4th, 2009 at 10:12 pm

   would a single charger, that allows you to select each type (AGM, gel, etc)of battery in each bank, work as well as having two independent chargers?

4. Jerr Says:
   November 5th, 2009 at 1:10 am

   Gerry – Glad you’re enjoying my blog and I’m happy to help. Tonight I put 7.5 gallons of distilled water in four 8D wet cells that have partially cooked, though they’re only nine months old: Everything has its price. Gels have a lower peak voltage and amperage; AGMs are intolerant of draining as gels are of overcharging but both won’t evaporate or spill. When I first sailed my Catalina 30, the wet cell batteries spilled while beating in a storm, making an awful mess. While I’ve had exceptional life from my gel cells, they’re 1994 vintage (15 years!) and are still good. I have not used them for high amperage uses and with their capacity (440 amp-hours for the two 8Ds), have enough of a pool to ensure they enjoy their leisurely life. AGMs would have not lasted anywhere as long as my house batteries because I draw them down sometimes when I’m cruising. If I started an engine with gel cells, they wouldn’t last long because they can’t supply that amperage without damage. Hence, the use of the best battery for the best purpose: Gels for house and AGMs for starters. Because they have such different charging characteristics, different chargers are best. The one problem is charging with the alternator, so I guess you’ll have to mount two engines or two alternators in your boat! Har har har! I treat my much smaller starter battery as sacrificial, so that’s how I deal with that.

   For those who aren’t familiar with Gerry’s project, check it out at http://theincrediblehull.blogspot.com. He’s an excellent shipwright, pretends he doesn’t know it and is building a beautiful, very well-considered boat.

5. Jerr Says:
   November 5th, 2009 at 1:12 am

   JC – Welcome aboard! If the charger really does have the capability of charging one bank differently, it’s an ideal solution.

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