More Power Scotty! Part Two

ScottyMorePowerIn our first post of this series, we told of our plans to transform the electrical system on Eagle Too to one suitable to support our five (or more) year mission of exploration and allow us to boldly go where few have gone before. In this installment, we begin the task. If you’re not in the mood for something long and a bit technical, perhaps you’d enjoy this LOTH classic from early last year instead: The Ocean Doesn’t Care.

Warning—strong opinions follow. Proceed with caution, your mileage may vary, check with your doctor before switching battery types, etc. etc.

Batteries. They’re the beating heart of a cruising sailboat. Responsible for providing the lifeforce (e.g. electricity) that powers the many essential systems aboard, their sudden or premature demise can leave the boat lost, dark and lifeless. If batteries truly are the boat’s heart, Eagle Too was unfortunately on the transplant list.

In an example of that strange but sadly predictable form of temporal distortion I like to call “Broker Time,” the listing broker who sold us Eagle Too described her batteries as “recently replaced.” In Broker Time, something that was done “yesterday” means a couple of months ago, “last month” means early last year, and “recently” means “That was so long ago I can’t exactly remember when.” So it was no shock upon examining the boat to find that our “recently replaced” batteries had 2009 date codes. But it wasn’t worth the trouble to make an issue of it, because we already knew we wanted to add a significantly bigger battery bank to support a Life On The Hook™.

Decision #1: What type of batteries do we want?

We didn’t have to devote much time to this decision. Flooded lead acid was the clear choice for us. Now I can say with absolute certainty that it’s possible to spend a boat load of money on batteries. But it’s not clear to me why anyone would want to. I realize that there was a time when solar cells were very expensive and very inefficient, wind generators were noisy and unreliable, a towed water generator will only work when you’re underway, and that’s just until a shark decides to have it for lunch, and installing an onboard diesel generator is just stupid expensive. Way back in those bad old days (let’s just call it the 20th century), the best solution for charging your batteries was to mount  the biggest alternator your diesel engine could handle and run your engine to charge when the batteries were low.  Unfortunately, this is very bad for your diesel engine. Running for long periods at light loads does not a happy diesel make. To minimize the engine runtime and make the most of the money spent on the big honking alternator, you’d want batteries that could bulk charge very quickly. A high charge acceptance rate I believe it’s called. The best ones to use were Absorbed Glass Mat, or AGM batteries. Then gel cells came along, and they became the next big thing. They have a higher acceptance rate than lead acid batteries, at three to five times the cost. But to save the engine all that wear and tear, they were possibly worth it.

But this is the 21st century, and the Chinese are cranking out cheap and efficient solar cells by the container ship load. Adding 200, 300, 400 watts or more of solar charging capability can be done in a weekend for one or two boat bucks. Wind generators have gotten quieter, to the point where you no longer have to anchor on the opposite side of the bay in order to not annoy the hell out of all your neighbors. Applying a little thought to your system design and taking simple steps like reducing your electrical demand by switching to LED lighting can probably result in your being able to harvest enough “free” energy daily to keep the batteries charged. Any deficit can be easily made up with a little run time on a portable generator (yes, I know the Honda EU2000i isn’t technically approved for marine use, but this has to be one of the most widely ignored strictures of all time).

If you’re not reliant on an engine-driven high powered alternator for the majority of your charging, charge acceptance rate becomes a non-issue. So why on Earth would anyone want to spend the small fortune that AGM and Gel batteries cost? I can really only see three good reasons:

  1. Space and access constraints. The batteries have to lie on their sides or stand on their ends to fit, which obviously isn’t going to work with a flooded cell. Or the location is very difficult to access, making regular battery maintenance difficult or impossible.
  2. You just don’t have the personal discipline to keep up on the maintenance (How hard is it to check the water levels monthly and add a little if necessary? But hey, kudos to you if you admit this shortcoming and have the money to buy the really expensive batteries to compensate).
  3. You have so much money to burn that you don’t even check the price of the things you buy for your boat. You just want the coolest, latest, bestest thing possible regardless of cost, like those blue underwater LED lights that make your boat look like the mothership from Close Encounters, or the remote controlled infrared thermal imaging camera that lets you see what your neighbors are doing on their foredeck after dark.

No, we knew we wanted to go with the flooded lead acid cells. Yes, you need to check the fluid levels occasionally, and it can be really bad news if you happen to submerge one in salt water. They’ll make chlorine gas, which will pretty much ruin your day, but at this point your boat is probably sinking, so the day is most likely already a write-off. Also, that’s why I’m personally not a fan of having batteries in the bilge. A minor flooding incident that can be stopped before the boat is at risk can conceivably become a lethal event. But they’re cheap, will last a long time if properly maintained, and you can do cool things like use a hydrometer to check the specific gravity of individual cells if you’re having a hard to diagnose charging issue (way beyond the scope of this blog post, some other time perhaps).

OK, so it’s definitely flooded lead acid. But what type and brand? Again, this didn’t require a lot of thought. First of all, we went with 6 volt golf cart batteries.  They’re built tough. I mean, have you seen the way some of those crazy ball chasers drive those carts? Jumping curbs, tumbling into sand traps, bouncing down fairways as they race to the 19th hole, those carts take a beating and the batteries are built to handle it. They’re also designed to charge quickly and deeply cycle repeatedly. As for the brand, while there appear to be a slew of different battery brands for sale at a wide range of prices, there are really only two or three companies that make batteries. They just put different labels (and prices) on them. For example, you can go to West Marine and buy some very expensive batteries for your boat. Or you can go to Sam’s Club and pay less than half as much. But they’re exactly the same batteries! They both come off the assembly line at East Penn/Deka. The only difference is the label. And the price. So not seeing the value in paying top dollar for a fancy label, we went with the Duracell branded 6 volt batteries (made by East Penn) at Sams.


One more quick word about golf cart batteries before moving on. There are in fact a few companies that make a premium battery, for a premium price. Trojan and Rolls are two of the names many are familiar with, for example. But in my opinion, the math doesn’t work. A gentleman who runs a marine service business whose opinion I’ve come to respect has done some pretty extensive testing on a variety of batteries, and he found that if properly maintained and charged, even plain old Walmart brand batteries will give five to seven years of service. If Trojans were going to last twice as long as Duracells from Sam’s, then I could see paying the premium price. But they won’t. If you’re lucky, maybe you’ll get an additional year out of them. Or maybe not. And for the 50% price saving (a Duracell is approximately half the cost of a Trojan), I’m just fine with my measly 215 amp hour battery rating vs. the 225 amp hour rating of the Trojan (Five percent more for only twice the price!).


With the batteries now on the pier, it was time to start the installation. In More Power Scotty! Part Three we’ll look at what was involved.

One thought on “More Power Scotty! Part Two

  1. Deb

    The only reason we were able to afford AGMs is that we ran across an East Penn salesman at The Annapolis boat show and he told us they often have “seconds” at the factory which have nothing wrong other than scratches or dirty cases. He gave us a phone number to call and we went the next day and picked up the batteries at more than 60% off. It turned out to be cheaper than flooded cells. AGMs are really the only option for us. Our batteries are impossible to access and they are also inside the living area where we didn’t want to risk venting fumes. Can’t say enough good about East Penn!

    SV Kintala


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