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As I type this I am listening to the drone of our Honda 2000 generator charging our battery bank. ZTC has 8 – 6 volt Exide golf cart batteries (lead acid) hooked in series-parallel giving us, what I believe is, 720 amp hours of power.

Note: If all this electrical talk is Greek to you, don’t worry. It is to me too and I went to college to study electronics!

Anyway, we have learned that well-taken-care-of batteries such as these tend to last on a boat about 5 years. Sometime a bit more if you’re lucky but also much less if they are not taken care of well. Ours are now 4 years old (there is a date stamp on them) and are leading us to believe that they are not doing so well. What are the clues?

  1. The voltage is dropping to 12.2 (this represents a 50% charge, the lowest we should let them go) each morning and occasionally in the evening as well. With zero load on them it “might” be 12.3.
  2. Some of the batteries look swollen.
  3. Some of the batteries require the addition of water more than I think they should.

Note: Lead acid batteries require distilled water to be added to them occasionally as it gasses off during the normal course of their producing electricity. Do not let the plates inside get exposed to air. Always use distilled water, never tap or water from the watermaker.

I have yet to check the specific gravity of each of the cells which, I have been told, is the only way to really know if they are screwed or not. I also could try to equalize them although doing so while not on shore power would be a pain (we would have to run the Honda for 12 hours or more straight, with us on board monitoring the situation).

We also might be able to get another year out of these guys but this leads us to a dilemma. Batteries such as these can be purchased at Sam’s Club in the US, and perhaps Puerto Rico, for about 65 bucks each. Down island, we are told, they are 160.00 each (our friend just bought some), 2.5 times more expensive!

Should we decide that we want to get new ones here, we could:

a) Sail back to Fajardo on the mainland, rent a car and go find a Sam’s Club.
b) Take the ferry back to Fajardo and try to organize the same (Did I mention that these batteries weigh about 80 lbs. each? Getting 8 of them back here on the ferry, IF they would allow us to do so, might be a bit of a challenge!)


c) Speak to Joe!

Yesterday we came across the sign pictured above and although he was closed at the time, we are optimistic. We’ll see what we can work out when we speak to him.

And just to add some variety to the post, here are a few pics taken by our buddy Jim during our sail from Luperon to Puerto Rico. Although you can’t tell from these pics, they were taken after our jib traveler self-destructed!


  1. Whatever you do, get them replaced. They aren’t going to get better. I’ve had great luck with Interstate 6 volt batteries in my off-grid home. 7-10 years, but that’s not bouncing around on a boat. Of course, you might have settle for whatever you can get.

  2. andy & sonja cru-zinacatamaran - Reply

    I take it although those are 6v batteries they actually run a 12v system, & if that is the case you can use 12v 110amp Deep Cycle batteries , how many amps are your 6v ? reading from what you have said you may actually have only 360 amp hours as they are 12v running, there for having 12 v 110amps it will give you more AMP Hours ,
    Plus if / when you replace them make sure they are all the same AMP hours & put some Greece on the terminals once connected this will stop / help the charge as well from being “broken” & corotion
    Hope that helps a little & Great pic’s of ZTC under sail

  3. Gosh, Mike, I would be worried about the swollen batteries. It looks like they are right next to the hull from the picture? If they explode, it would not be pretty. How far back is that Sam’s Club?

  4. Just be glad, Mike, that you don’t have 8Ds (typ. 76 kg / 170 lb each)!

    Batteries are a complex subject, and the exact cause of a failure is often hard to find. Yours evidently aren’t holding up as well as they should- I would consider five years of intense but well-cared-for service to be the minimum acceptable. 5 years is 1826 cycles in continuous use, which any good deep-cycle battery should be able to handle on a typical 50% to 80% cycle depth with regular equalization and 100% top-ups.

    The fact that yours are starting to act up so soon- it looks like they were made in Feb. 2008- would suggest that your charger’s programming isn’t very well matched to the battery bank. I’d do some serious investigation here, to find and fix whatever problem is killing these ones, before the same happens to their replacements. A clock, thermometer, ammeter and voltmeter are all you need to map the charging voltage and current over a full charge cycle, keeping an eye on the battery temperature- it’s boring work, but having the voltage/time and current/time curves will let you see what the charger is doing and, hopefully, what mistakes it’s making. (Virtually all chargers need some degree of tweaking and reprogramming; the default configuration is rarely optimal.)

    I’ll end with a link to a John Harries article on how to keep these buggers happy in the long term:
    And I’m sure you’re making good use of Nigel Calder’s “Boatowner’s mechanical and electrical manual” here too.

    • The batteries are also stamped jun-07 (on the side) so I assumed that was the date of manufacture. The boat never had a real battery monitor before I installed one so I am SURE they were not charged as they should (deep discharged too frequently and too much). I’ll check out that article. Thanks.

  5. I would stick with the golf.cart batteries. They will last longer and can handle more deep discharges. I just replaced my bank of Trojan T-105’s which are 225 amp hours each for about $80 each here in the states.

    Which ever way you go let me make a suggestion, take pictures of the bank as it wired today. Maybe even sketch the configuration including pos and neg of each battery. This will save a lot of hair pulling later.

    Fair Winds.


  6. Mike, we replaced our batteries in Luperon, found a very good deal on them, much cheaper than in PR. We installed Trojan T-105 batteries, 225Ah. Since the DR is in the wrong direction 🙂 … you should do some online shopping at Budget Marine. We did a bunch of provisioning in St. Maarten and found them quite reasonable (google Budget Marine St Martin). They list the T105 for $170/ea … they probably will do an additional discount (did for us).

    I love our new batteries, great reputation, solid performance … we replaced 6 of the “others” for 4 of these … no regrets.

  7. Where are they stashed? I take it the area under the step is full (I keep fishing gear and tools in there)?

    Your AH calculation seems right; add them when parralel, but not when in series. I’m jelous of the total; I have only 270 AH in 3 group 27 batteries. You’ve chosen well.

    I don’t see cases. I guess that is not so bad, if they drain overboard and are separate from the cabin (not for monohulls!), but would be careful what I put in there with them. For example, an acid spill would eat through a gasoline line, one reason the code forbids placing batteries above fuel tanks and lines. Also, mixing gasoline lines and batery cables is very bad practice; Iv’e seen a number of bad fires cause by chaffed cables lighting fuel lines (trucks).

    I’ve never know batteries to come back from faded like that. The truth is that killing them just a few times makes a big difference, so life is hard to judge.

    I like the battery store, if just for the expereince!

  8. Specific gravity testing is useful but if you want to know what you’ve got, they need to be load tested. Hopefully Joe can assist with that. If he can’t / doesn’t load test them, then be wary of his opinion(s).
    Maybe this will make you feel better. Our 5 Odyssey pc2250 batteries

  9. Hi Mike
    I have replaced my 6 battries with t-105’s. Thats what was in the boat when we bought her.
    The price in Canada is $160.00 each. Someone posted that they bought them in the US for $80.00. I think Trojan is making a little extra selling them in Canada!! At $80.00 there giving them away.
    Of the 6 battries 3 were 9 years old. I had two that were 8 and one at 6. The 6 year old was killed by the older ones. I was told to replace them all at the same. They are only as good as the weakest link!!!!

  10. Like Matt said, equalization is certainly a key. T-105’s work very well, and if it wasn’t mentioned, investing in Hydrocaps is a pretty good idea as well. A Hydrocap is a catalytic gas recombiner than converts hydrogen and oxygen gasses into pure water. A catalyst is a substance which encourages other substances into chemical change without actually participating in that change, sort of a chemical ambassador. The process occurring in the Hydrocap is similar to that occurring in an automotive catalytic converter.

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