Wednesday, May 07, 2014

Batteries, and Battery Types

New Bern, NC
35 06.670 N 077 02.371 W

Sigh, it's time to buy new batteries again.  It seems like every other week, (but of course, that's not true).  One of my two batteries has two bad cells.  The other is about the same age as the first.

I have a single bank of two group 31 batteries, no starting battery.  Also no room for four batteries.

I'm wondering what replacements to buy.

Gel Cells --  Early on Tarwathie, I bought gel cells.  They were a disaster, failing almost immediatly after installation.  I went through 4 sets in 18 months.  Unfortunately, for West Marine, they replaced them four times under warranty.  I sold them to another cruiser, and he replaced them within a week free at West Marine after I provided him with my receipt.   I finally figured out that my engine compartment runs far too hot (about 140 F in summer) for gel cells.  My conscience felt bad about that, because the whole thing was my fault, not West Marine's.

AGM -- These batteries cost the most, and many people assume that they are the Cadillac of batteries simply because of their high price.   Actually, the primary advantage of AGM is that they can accept charge more rapidly.  But to take advantage of that I would have to double the capacity of our alternator, double the capacity of the shore power charger, install double pulleys on the engine for the alternator belts, and buy an electronic charge controller, and install engine room ventilators;  a lot of stuff.   The reality is that when we run the engine on the ICW, we run it 10 or more hours per day.  When not on the ICW, we use solar panels for recharging, not the engine.   AGMs for Tarwathie would costs a big pile of money for little advantage.  Also, I can quickly think of three or more cruising friends, who had horrible experiences with AGM batteries.

Flooded Cells -- Conventional batteries are best for Tarwathie.  But recently I went to a battery seminar sponsored by Trojan Battery Company.  They made good arguments, as to why their premium brand was better.

Today, I went to the local battery store to shop.  First, I found that Trojan group 31 batteries cost $240 each, compared to $120 for regular brands.  Double!   The warranty on Trojans is the same one year as on the others.  Trojan claims that you might get 60% more life with their batteries compared to brand X, but they won't warrant it.  Sounds like double the cost is hard to justify.

Then, I learned something new.  The dealer was selling dual-purpose batteries.   They are halfway between starting batteries and deep-discharge batteries.  I never heard of that before.   I run a single bank for both cranking and house loads. I used to have a separate starting battery, but I junked it after nearly 5 years of almost never using it, because it was so inconvenient using the battery switch to select the starting battery to start.

I'm skeptical of dual-purpose batteries.  What do my readers have to say?   What do they say about me using my single bank for both cranking and house power?   Normally, my engine starts with less less than 1 second cranking.


  1. Dual purpose batteries are truly the bastard children of the electron storage world. Almost certainly built simply for marketing purposes, they neither provide CCA nor do they cycle deeply, achieving crappiness at both jobs they are "designed" to do.

    For small diesel engines like the Beta38, a deep cycle battery can easily provide the cranking power required and there is no real need to get a big starting battery that is expensive. Personally we went with 6v batteries and they are working great. We got ours at Sam's Club for 70 dollars a piece, so that is 140 bucks for a 12v battery. It pays to find out who manufactures the batteries despite the branding.

    1. On Neverland we replaced our batteries with 3 dual purpose 12v, 100 amphr, lead acid types at about $100 each. They were recommended by the local charter fleet, I suppose because they can tolerate some maltreatment and are otherwise cheap to replace. We're starting our 7th season with the same batteries. We periodically "condition" them, which may help with longevity.

      Of course we only use them for about 5 months during our sailing season, but they must survive Duluth winters with 20-30 degrees below zero and a solar trickle charge.

  2. I've been off-grid at home for 30 years and use 6 volt, 210 amp-hr golf cart batteries. Also have used a pair of these on boat for many years. Much better than deep cycle/starting marine battery which is a little bit of each.
    On boat also have a car starting battery though seldom use it....its my insurance in case the house bank gets too low (never needed)


  3. Robin has two (group 27 or 29, I think) batteries. She had two golf cart batteries when we bought her. For the limited cruising we do, these two Group batteries work well. I think I've replaced them twice in ten years. I'm in the midst of rewiring and plan to have one cranking battery and 2 house batteries to increase amp hours (a concept I understand only when I've just re-read the 12-volt book) so that I don't have to be concerned in the middle of the night about the anchor light and the refrigeration running simultaneously. (I'm also replacing all light bulbs with LED.)

  4. Orion uses 6V golf cart batteries for its house bank as they were specifically designed to be discharged and then recharged at a later time. Several years ago, I saw a study that showed them to provide the most amps/dollar. Also, they can be easily replaced at remote areas as there are almost always golf carts nearby.

    My first set were Trojans based on all the positive press, but as they became so much more expensive, I switched to Sam's Club batteries. I can't say that I've seen any real difference between them other than price.

    When we started cruising, we always started Orion on the starting battery, which is a less expensive Group 24 Walmart gold (?)battery, which carries a 3 year non prorated warranty. Note: This battery lasted 7 years. However it didn't take us long to stop switching the battery banks and always start her on the house bank. This left the starting battery always at the ready, but never used.

    The only draw back to starting the boat on the same battery bank being used for everything else (either of the above procedures) was the low voltage impact to our electronics. Although we started this way for several years and I never saw any real negative impact to my electronics, it still bothered me. Therefore, I did some rewiring.

    Now I have my engine directly connected to my starting bank and my house bank directly connected to everything else. Since my alternator charges the battery bank used to start the engine, I installed a Blue Sea Automatic Charging Relay between the two battery banks. Now the boat starts without my electronics experiencing any voltage drop and both battery banks are charged without flipping any switches. While I still have the ability to throw the battery switches in case one of the battery banks fails, I doubt that I will need to do it.

    Given that you are accustomed to a single battery bank, I would convert it to 2 golf cart batteries and live with it unless your electronics detected otherwise.

    PS: Orion Jr. has a single battery bank of 2 Sam's Club golf cart batteries and we simply don't turn on the electronics until after we start the engine. In an emergency, I can always pull her starting cord to start the engine.

  5. The market for batteries and chargers is extensive. I'm sure you're quite experienced on this front, since you deal with them everyday. As for dual-purpose batteries, think of it as a compromise: while you're not getting the best deal on either option, you're still getting the both their functions for versatility's sake.

    Keith Edwards @ Apex Chargers


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