New Battery Box

Sometimes I think I should rename this blog “stupid ways I’ve cut plywood” or “How to Make Sawdust.”  It often takes me one complete failure in order to understand how to do a project.  I amaze myself.

Anyway, I built a really nice plywood battery box for my new (to me) batteries.  My boat neighbor was gifted a couple of gel batteries last year, and he in turn gave me his not-very-old group 29 Interstate deep-cycle batteries (two of them).  It was a timely gift, because I was planning to buy a new set of batteries in very short order, and to build a new box for them.  I currently have group 24 batteries – unaltered since I bought the boat 10.5 years ago – sitting loose in plastic boxes with the covers held on by a shock cord. These aren’t the original batteries – the way they are installed is original. I’ve never liked it, but didn’t change because. . . um, I just didn’t. Now that it looks like we might take longer, more adventurous trips, it seems important that the batteries are installed properly. To that end, I built this box:

DSC_3211 DSC_3212

No, it is not marine ply.  I don’t have a truck with which to haul a full sheet of plywood, and I don’t want to pay $95 a sheet for it anyway.  I’ll epoxy and glass this box, and it will be fine.  Well, not this box.  You see, it’s too small.  Group 29s won’t fit in there, even though I measured carefully.  How did this happen, you ask?  Well, never mind.  Suffice it to say, that I was under the impression that the box had to be sized just so, and I indulged in a folly of false economy.  But it’s a nice box.  For something. . .

I bought more plywood this morning (Home Depot sells 2×4 pieces and they fit in the back of my car), cut it correctly (this time – numerous mistakes on the first box), and put it together this morning.  By lunch time, I was letting the glue cure.

Pile of pieces.

Pile of pieces.


I also decided to just make the box square – simplifies the carpentry a good bit. The larger box on the left is the one I built today.


Later in the day I rounded off all the corners in preparation for glass/epoxy.

I’ll glass the box inside and out in the near future, install studs along the top edge to secure the top (with wing nuts), cut out wire relief slots, and it will be ready to install.  It will be bolted to two adjacent bulkheads in the starboard cockpit locker, painted Bilgecoat-grey, and filled with batteries.

  1. Anonymous said:

    I can feel your “pain” about having to re-do projects, due to “simple” miscalculations, LOL. The new box looks good though.

  2. Thanks! I know I’m not the only one who struggles with this, but when I’m in the midst of a blunder, it feels like it.

  3. Anonymous said:

    Rick, what height dimension did you use to still be able to get it through the locker access? 11″? 10″? Less?
    Also, I guess, why did you feel the need to craft a top for the box? To keep the batts from bouncing out of the box in heavy seas or just what is your worry scenario? Guess I just figured the weight of the batts contained in the high sides of the box and bolted to the bulkheads would be enough insurance. Probably wrong though.
    Looks like a good project for me too since my batts are just strapped down now as yours were. Thanks. Greg

    • Honestly, I didn’t even think about getting it through the locker gap. Don’t think I’ll have a problem though. The box is 16.5″ square, but 9.5″ tall. There’s plenty of room to slip it in sideways. Also consider that I have the face of the locker cut out for improved access – to within 2″ of the cockpit sole.

      The top is – (I’m pretty sure, but haven’t checked the relevant resources) – a USCG requirement, and is certainly strongly suggested by ABYC guidance. I think the presence of sulfuric acid electrolyte is enough justification for a top, but my primary reason for the top was to restrain the batteries from movement in the event of a knock-down. This can happen inshore just as easily as off-shore. Although I don’t have any evidence that the batteries have ever moved significantly while sailing (they weigh 50# each, after all), I’ve never had a knock-down either.

      Allowing them to lie loosely on a shelf in the cockpit locker defies common sense. They should be restrained, as something that heavy thrashing around during a knock-down would cause considerable damage. I’ve been lucky for 10 years. . .

  4. Anonymous said:

    Thanks, Rick. Didn’t know about your cutout, but the 9.5″ dimension sounds like it’d slide through the locker hatch for sure. Also didn’t know about the lid requirement, but it makes sense even though the CG has inspected me and didn’t say anything (guess they had other things on their mind that day). So you’ve probably saved me a citation some sailing day. Hopefully you’ll allow me to take a look at your boat and all your improvements during the upcoming raft up so I can quit pestering you with clarification questions. Appreciate it. Greg.

    • Greg, Like I said, I’m not sure about the USCG requirement. You should check if that makes a difference to you. Also, if you are coming to the raft up, and are using group 24 batteries, the first box I built will probably do the job – I’ll bring it with me and you can have it. If interested, I’ll send you the inside dimensions so you can confirm the fit.

      I don’t mind the questions. It’s fun to talk about boats!

      • Anonymous said:

        Thanks much for that, Rick. I believe they’re group 24, but I’ll double check the group tonight when I’m back at the coast and let you know by tomorrow. Greg.

      • Anonymous said:

        Rick, you’d think I’d remember by now, but I double checked in the dawn’s early light and the two batts are group 29. So I can’t use your spare, but I sure appreciate the offer. Could I maybe get you to blog post the dimensions you used for the second box so I can dupe it and not make my own spare? Thanks again. Looking forward to my first raft up and meeting you and all the folks.


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