Battery bank replacement: power projects aboard

17 Apr
Battery replacement project

More than six months ago our battery bank ticked past the five year mark. That’s a pretty good life for marine AGMs, so we’ve been thinking for a while about where and how it would be replaced. You can’t always count on easy access to boat bits in the islands of Southeast Asia, so the big concern is that the bank would nosedive in an inconvenient location with complicated and costly results. We wanted to wait as long as possible, but expected it to become necessary at any moment, making it the top priority in a string of power projects on Totem but one that hung in the air for several months.

Battery replacement project

What we put in
Battery replacement project
Totem has AGMs (Absorbed Glass Matt), the deep-cycle sealed batteries commonly used on cruising boats. As we talked to other cruisers in the area, many reported good results with AGM batteries sourced from a local manufacturer. Good batteries, fresh from the factory, with minimal shipping cost (heavy batteries can make it absurdly expensive): a perfect combination. We just had to make our existing bank last long enough to get to the Malay peninsula!

When they finally arrived, it took a couple of dinghy loads to manage the weight. Each one is heavier than Jamie! Thank goodness for friends in the cruising family to help get them on board. If you’ve been on Totem’s Facebook page recently, you already saw how handy the dinghy davits were for loading these monsters on board. They came in really handy, not just to have purchase on the weight, but because could swing them out over the dinghy, then back over the deck, vastly simplifying the transfer.

Tweaking location

Moving weight on the boat was a meaningful side benefit of the project. Totem has listed slightly to starboard since we bought her in 2007. This is primarily the result of tankage being moved around from the original plans, skewing weight on the starboard side. Our house battery bank was also located on the starboard side, just under the nav station (photo above). For the new batteries, Jamie built a box under our bunk in the aft cabin. This would create a significant weight shift: with about 400 lbs coming off the starboard side, and over 600 going in just to port, we might just get a flat boat.

Battery replacement project

Of course, it’s never as simple as just building a box. Over a period of several weeks, Jamie built out the box for the new set under our bunk: grinding down fiberglass (wow, that’s a lot of fine dust), fitting lumber to make a strong base (discovering the many lumber yards on Langkawi!), and building the frame up (I love the smell of polyester resin in the morning…not) to securely hold the new bank. It was a lot of work.

Battery replacement project
before wiring, double-checking with Calder

What about Lithium?

Lithium batteries are getting more common on boats and we’re familiar with some installations that get raves from their owners, on the yachts Tahina and Nimrod. They have some great benefits: because they can be drained more deeply (and charged more fully) without affecting their lifetime use, which provides far more usable power for the same total amp hours in a bank. Their lifetime value- amps delivered vs cost- is superior. This saves weight, too, a meaningful factor on some boats.

On the other hand, they have a higher upfront cost. In addition to the battery cost, we’d have to take on additional projects. We’d need to make sure our alternator was big enough (it probably isn’t). We’d need to check the voltage requirements of every device on the boat, because unlike AGMs and their ilk, lithiums can put out higher voltage- over 15v- in a 12 volt system. For voltage sensitive devices like our watermaker, we’d have to put in a regulator.  Maybe in five more years we’ll move to lithium batteries, but it’s too much to take on now.

It’s all good.

The new bank is 1000 amp hours, a nice bump in capacity that we definitely need. Totem is floating- dare I say it? nearly level on her lines. I don’t get to examine the waterline often, but every time I melt butter in a frying pan and don’t see it all run immediately down to one side, I’m going to smile.

Battery replacement project
Amped up readers know we get a charge out it when you read this on the Sailfeed site.

This article was syndicated from S/V Totem - a family sailing the world


  1. Chauncey M Freeman,SCPO,USN,RETIRED


    I love reading articles written so as not to require the reader to be an engineer to understand. Thank you also for the BUTTER TIP, or I suppose one could call it a Butter Jig. Anyone having a hands on knowledge about boats knows that there are many times when we are the inventors of new, but functional Jigs. Keep on enjoying your life aboard and be sure you keep the most important Repair Manual aboard, the King James Bible.

    Senior Chief Chauncey M Freeman,U.S.NAVY,RETIRED

  2. brian tennant

    good job, wodering if i need a new set, will i be able to aquire in maybe kota kinabalu. and what was the costing

  3. Melissa White

    We just took a look at the AGMs in our boat and realized they are pretty old. On the other hand, they are still holding a charge really well. I suspect it’s because they haven’t been used much for several years since there is really nothing on the boat that creates a serious draw of power right now. Hoping they will last us until we’re almost ready to go a-voyaging, then we can replace them. We’ll keep an eye on how you like the ones you bought. Nice to have a level boat!

  4. Seven Cs

    Ooohh – grinding fiberglass inside the boat doesn’t sound so fun. On the other hand, 1,000 amp hours of battery and a level boat – that sounds fun :)

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