Battery Cables

Making a custom length battery cable takes a drill, mini-torch, crimper dies, flux, and solder.

We do lots of custom electrical work in the fab shop, and one job that seems to come up all the time is making custom battery cables. Trying to find ready-made cables that are exactly the right length is difficult at best, and damn near impossible for those extra-long cables when your battery has been moved to the trunk. Given the weight and cost of heavy gage copper cables  we make our own, using SAE-rated battery cable, and heavy-duty cable lugs to get exactly the right length.

We modify the lugs by drilling a 3/16 hole in the end to push in solder.

A failing battery cable is a big problem, so we both crimp and solder the lugs to the cable. The soldering is done after crimping so we drill a hole to feed in solder. We drill first because it’s easier to manage the lug without the heavy cable already crimped in place.

We can’t remember where we got these heavy duty large-gauge wire crimping dies which work well enough, but for bigger jobs we use a hand held hydraulic model.  If you are on a budget the Harbor Freight product will get the job done for a home builder.

After stripping the insulation, and coating the exposed wire with flux, we insert the cable into the lug so that the insulation goes in about an 1/8″. I use these crimping dies in a vice with a 3 ft cheater bar. It’s a four handed operation to get everything lined up and the vice snug to begin the crimping operation, so a helper is important.

A butane mini-torch is required to get enough heat into the lug and wire to get a proper soldered joint.

After crimping, it’s solder time. We use a butane mini-torch (an electric solder gun just can’t generate enough energy to heat that much mass), and heat the lug until we can push the solder into the wire inside the lug, making sure we get solid solder bond. It’s tempting to feed too much solder into the joint, but don’t: too much solder will wick up the wire past the joint and make the wire stiff, which can eventually cause failure. 4 or 5 inches of solder is about right.

The end product, showing the crimp and solder.

The soldering operation partially melts the insulation at the edge of the lug. This causes no harm, and can be covered with some large diameter shrink wrap, trimmed with a sharp box cutter, or left as is. The metal discoloration is caused by the flux, and wipes up easily with some acetone or similar solvent.

7 thoughts on “Battery Cables

  1. Nice! I’ve tried different approaches and was never really satisfied with the results.
    Thank you for sharing the right way to do this.

    -Philip

  2. Most folks would just settle for a crimp, but the method shown will have zero chance of pullout. My experience is sealing the connector near any battery posts is critical for long term reliability, and the solder method shown works fine. The other way to do this would be to put connector in vise and heat the barrel with a torch [mapp gas works well] and fill halfway with 50/50 solder: when it appears to lose it’s film/no solids floating on top, it’s hot enough to plunge prepared cable in place. Scoring the inside of connector lightly with 120 grit and using a light coating of resin flux on both connector surface and bare copper strands beforehand will allow it to wet easily and drop in quickly. Finish off with a little heat shrink tubing to seal the remaining exposed copper from future battery gases or unplanned spillage, and never worry it about it again.

  3. Pingback: Main battery cable ... Butt Connector? - Page 2 - The Hull Truth - Boating and Fishing Forum

  4. Here’s a little secret I’ll let you in on; I have been using welding cable. It has a few properties you should consider. It has a higher, more pure grade of copper inside and the outside cover is rubber. Rubber is much more pliable, especially in colder weather and safer. You can purchase it in just about any length and isn’t too much more than
    battery cable. All in all, it is a terrific upgrade.

    • Steve, thanks for posting!

      Welding cable is indeed more flexible when compared to SAE (SGT/SGX) battery cable. However (as you’ve pointed out) it is more expensive, and worse than that, battery cable isn’t rated for oily environments. The insulation will swell when in contact with oil. I can’t recommend its use in automotive applications, especially under the hood.

      Perhaps using it inside the car for trunk-mounted batteries would be fine.

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