Battery Cable Crimping

How to Properly Crimp Battery Cables
Step by step With Pictures & Video


We will teach you how to properly utilize a hydraulic lug crimper in order to create a strong, low-resistance connection that will not only last for years, but also will reduce the risk of fire or property damage due to an incorrectly terminated cable. In our example shown in the pictures, we are replacing an existing piece of Aluminum wire, with our newly made properly crimped copper cable!

Tools & Materials Required:

Video Tutorial

Step 1: Determine Cable Length

First, you will want to determine how long of a battery cable you need. Often times to determine cable length, it is easiest to just hold the cable at the starting point and imagine the run to the finish point, while still taking into account the amount of cable that goes inside of the lugs. Alternately, a measuring tape may be used if this proves to be too difficult.

Step 2: Cut Cables to Length

We used our Klein Journeyman cutters, which are great for this use. Even though this cable is outside of their typical cutting range, they were still able to cut through. Don’t let the picture fool you. There’s no cutting through this monster of a cable by hand. We ended up standing on the cutters in order to get through this cable.

Step 3: Mark Insulation Strip Length

The easiest way to determine how far back the wire will need to be stripped is to hold the wire next to the lug. Locate the end of the wire at the point of the lug where it starts to taper down to the flattened area. Make a mark at the open end of the lug, compensating that some of the insulation will press against the lug. Make sure not to strip your wire too long – Exposed copper is not desirable. Too short of a strip length will not allow enough wire to enter the lug for proper crimping.

Step 4: Strip Insulation

This is not a job for conventional wire strippers, side-cutters or cable cutters. Use a sharp knife to cut 3/4 of the way through the rubber insulation. Make sure to avoid cutting all the way through and touching the copper; it is extremely soft and the fine strands are easy to nick with a knife. Nicking the copper can turn into a weak spot in the connection, leading to failure in the future. This is especially true for smaller gauge cables that utilize finer strands.

Step 5: Remove Insulation

Since we are already partially though, you can now bend the wire at the score line and the insulation should break and seperate at the slice. If it doesn’t break, you can lightly touch the knife against the rubber that is still connected. Once fully seperated, simply pull on the section of insulation to be removed until it is clear of the wire.

Step 6: Insert Wire & Ensure Fitment

With a lug that corresponds to the wire size, inspect for any defects or oxidation. If it is oxidized on the inside for any reason, you should consider using a different lug; if one is not available, you can scuff with either some fine-grit sandpaper. Any oxidation can increase the conductivity of the termination and lead to heating and catastrophic failure. Slide the lug over the stripped end of the wire and make sure that the proper amount of insulation is stripped back (no copper exposed.)

Step 7: Prepare Crimper

Our hydraulic crimper comes with a variety of die sizes. Unfortunately the die sizes are in mm² so a conversion chart is required (available online). After installing the proper dies, you must check to ensure the release valve is closed. In our case for 4/0 AWG we found the 95mm² die made the best crimps, but results may vary.

Step 8: First Crimp

With the wire fully inserted, place the lug in the crimping tool with the dies aligned as close to the open end of the lug as possible. Begin closing the dies by actuating the pump, until slight pressure is placed on the lug, but not so tight that the lug can’t be rotated. Orient the lug as shown on the picture.

Be Careful As you are crimping

Make sure the wire is properly inserted into the lug. Maintain pressure on the wire during crimping. If the wire is not fully inserted, a proper crimp will not be established.

Step 9: Finish Crimping

Our hydraulic crimper comes with a variety of die sizes. Unfortunately the die sizes are in mm² so a conversion chart is required (available online). After installing the proper dies, you must check to ensure the release valve is closed. In our case for 4/0 AWG we found the 95mm² die made the best crimps, but results may vary.

Step 10: Second Crimp

Place the lug back into the crimper, this time on the remaining area that was not crimped during the first operation. Continue crimping just like before. Once completed, pull on the wire to make sure it does not come out of the lug.

Step 11: Success!

If your cable looks like ours, then you have successfully crimped your first lug! You can now proceed to the other end of your cable.

Precaution: Rotation!

Pay extra attention when crimping the lug on the other end of the cable; with thicker cables, you will not be able to twist the cable to compensate for an improperly oriented lug. If needed, make a mark on the wire and lug to note where to line things up during crimping.

Step 12: Second Lug

With our orientation established, we can align our marks and crimp the second lug on the cable. Just like before, ensure the wire is fully inserted before crimping.

Step 13: Test Fit

Now that the crimping has sucsessfully been completed, test fit your cable to make sure proper length and rotation have been achieved. If everything checks out, we are ready to move to the next step.

Step 14: Heat Shrink

For our 4/0 cable, we are using a heat shrink tubing that is a 3:1 shrink ratio. When the tubing is flat, it measures at 1 1/2″ wide, and we cut a 3 inch long piece for each end. Smaller diameter cables can have shorter lengths of tubing. The goal here is two fold; reduce the stress from cable flexing from fatiguing the crimp, as well as preventing moisture from entering the crimp and causing oxidation.

Step 15: Heat Shrink Continued

Begin heating the shrink tubing with a heat gun. We have a wide tip that spreads the heat out across the entire width of the shrink tubing. Continue to turn the cable to apply heat consistantly around the whole circumference of the tubing.

Step 16: Completion!

If your cable looks like ours, then you have successfully completed this cable. You may now install your cable – Make sure that the bolts or nuts are tightened to their proper torque ratings.

Frequently Asked Questions & Considerations:

• Should I solder my lugs after crimping?

In marine applications solder joints are forbidden and in most jurisdictions residential and industrial power circuits, soldered joints and lugs are not code. The reasoning is that if the conductor is overloaded, the solder would begin to flow and the juncture would overheat catastrophically. For parts subject to flexure and vibration, solder can wick into the strands past the crimp and the wire will eventually work harden and break just past the lug. In marine environments the dissimilar metals of the solder lead/tin/zinc to the copper just adds more issues. Best is a quality lug, quality fine strand tined wire, quality crimp, with adhesive lined heat shrink tube. Studies have shown that a proper mechanical crimp using a hydraulic tool can “cold weld” copper to the terminal, creating a superior connection compared to soldering.

• Do I need heat shrink tubing that has glue on thie inside?

Shrink tubing that has glue inside will provide a superior seal. We highly recommend this type of seal for marine applications or environments that have high humidity. It ultimately comes down to personal preference and evaluation of the installation environment, as well as how long you desire the connection to last. Terminations that utilize top-quality components will last the longest.

Video Tutorial & cross section sample