Extra Boat Battery Post

I'm not a fan of expensive batteries. They've led me astray one too many times. I bought a $300 AGM battery with a 2 year warranty. Twenty six month later it bit the dust. Today, I buy an El-cheapo for the boat and replace it immediately after the first sign of trouble -- whether it's under warranty or not.

So, it's Walmart batteries for me. My boat had a deep cycle for it's house battery when I became the new owner. That battery crapped out minutes after I took possession. I replaced it with a Walmart Deep Cycle Marine battery...which lasted a year beyond it's one year warranty.

Automotive batteries have a 3 year replacement warranty and 5 year prorated warranty. Why would I buy another marine battery when I could abuse a car battery and get it replaced for free if it failed within 3 years? So, instead of a deep cycle marine battery, make that a car starting battery.

The trouble is, the starting battery has only a single clamp style post, while my deep cycle battery had both the clamp and wing nut posts.

 I had my bilge pumps and propane monitor wired to the wing nuts and now there's no place to put these eye terminals.

The redneck solution is to back off the clamp nut on the battery clamp and put the ring connectors between the clamp and clamping nut (and I've used this on occasion). I don't like this for three reasons:
1) I hate to mess with the clamping system because if you run the clamping nut in too far it distorts the clamp and you've got to really snug it up to ensure a good connection of the eye terminals.
2) The heavy eye terminals take too much room on the clamping bolt -- so the nut doesn't fit.
3) If you use the redneck method for the eye terminals, every time you mess with the battery, you undo that connection.

The next quick solution is to get a 5/16" square nut and a 2" 5/16 bolt. Put a washer on the bolt - put the eye terminal on the bolt, run the square nut up to the eye fitting and tighten it, then put the bolt in the clamp.

 This lets you use the square nut against the flat on the clamp to allow a snug fit on the battery post.


But I like complete flexibility so here's what I suggest:

Get hold of a 2+" X 5/16" carriage bolt and a square nut for same.  Carriage bolt because they are usually threaded the entire length.

Cut the threaded part off at about 2". This will be your new clamp bolt.


Run the square nut down the new piece until there's an inch of free threads on one end.

This is where the nut is to be fixed to the threaded piece. I brazed my nut to the piece, but solder or even Loctite thread lock will do.

Remove the paint from the existing clamp where the fastener exits...on both sides of the clamp. I used a file, but a wire brush on a drill would work just as well.The clamp is soft lead, so this is very easily accomplished.

Now substitute this new piece for the old clamping bolt and you'll have a permanent place to attach those eye fittings without distorting the clamp or needing to mess with terminals when the clamp is removed from the battery.

BTW - if your square nut doesn't fit nicely against the flat of the clamp, try rotating the nut to a different side -- or just file away a little of the flat part of the clamp.


And a little chuckle here for my senior moment. The original design wasn't quite so simple. I used the existing clamp bolt and brazed a short piece of threaded stock to the head. I even drilled the head of the square bolt and machined a pin on the threaded part to make it easier to braze. When I got it all together I realized it's just a square nut on a piece of threaded rod!