Tuesday, July 23, 2024 Detailed Auto Topics
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Battery terminal corrosion is quite common.  Not only is it damaging to the battery terminal and cable it can cause problems you might never expect.  Simply cleaning it off is temporary at best and can cost you a bundle.

Corroded battery terminal caused by leaking battery post

Battery terminals corrode because acid and hydrogen gas leaking at the base of the battery post react with the metal in the terminal.  Corrosion eats away the metal and causes high resistance in the battery circuit.  Cleaning away the corrosion does not correct the cause.  Batteries with leaking post are often covered by the battery warranty.  Replacing the battery is needed to stop the problem. 

When the terminals are damaged, replacement of the cable and/or cable end is needed.  When cables are inexpensive and easy to replace, a new cable is the way to go.  More and more, cables today are part of the wiring harness, very expensive and difficult to replace.

Clamp on battery terminal endMany times when cables are damaged, people are tempted to install bolt on battery terminal ends. High resistance can form in the clamped together joint. Resistance can interrupt flow of current and cause a huge amount of problems.

For example, a starter motor may pull two-hundred amps when cranking the engine. This current comes from the battery and must return to the battery. If a bad engine ground cable is incapable of transmitting this current, it must find another way back to ground. This is called a transient ground, electricity flowing through components other than the battery cables.

The engine sits on rubber mounts which cannot conduct current. Instead it can flow through the engine block, into the transmission and out to the suspension through the drive axles to the body ground. These parts are not designed to conduct electricity and can quickly be damaged by the flow.

Another problem is flow through the engine coolant to the radiator and heater core. This can cause electrolysis and very quickly destroy a radiator, heater core or even an engine block.

How much resistance is too much?

According to Ohms law, Amps X Resistance (in ohms) = Volts. 

With a 200 amp circuit, just .02 ohms of resistance will result
in a four volt drop in power.  This means only 8 volts is available
to run the vehicle and computer issues, damaged starters and
alternators can result.

A proper cable repair starts by installing a back-up power supply to the vehicle. This auxiliary power source will help prevent loss of memory in the power control module (PCM) body control module (BCM), security system and radio pre-sets.

Auxiliary power applied to prevent computer memory loss

Disconnecting the battery without auxiliary power will cause the loss of diagnostic information and the emissions "readiness" test. These can take a week or more to rebuild. During this period the vehicle will not be able to pass State inspection. Loss of adaptive learn can also result in poor idling and transmission shifting concerns.

Next the old corroded end is removed and insulation is stripped back from the wire ends. The wires needs to be closely inspected for acid damage.  Often acid will wick up the cables inside of the insulation. When this happens the cables are damaged and must be replaced to a point beyond where the corrosion exist.

New battery terminal added to cable and ready to be crimped

 If needed a new section of cable can often be spliced into the old cable to replace the damaged section. If the cable is okay, heat shrink tubing is placed over the ends. The bare wire is then inserted into a new terminal end.  The assembly is now ready to be crimped together. 

Battery cable terminal crimping tool

After the cables are inserted into the new terminal, a special crimping tool is used to firmly attach the new end. This tool forms a permanent electrical connection between the wire and the cable. This type of joint is exactly the same as the factory cables that come with the vehicle.

Other than lower cost, such a tool allows additional grounds to be added if needed. It also allows for better than original terminals or special terminals to meet specific needs. Larger than stock wire can also be added if found to be needed.

A properly repaired battery terminal

Once crimped, the heat shrink is slid into place and shrunk to seal the connection. This provides protection and helps keep corrosives from damaging the joint. A new bolt and nut are installed and the terminal is tightened to the specified torque. This completes a job which is often better than the original cable.

The final repair is attractive, permanent and most important, electrically sound.  Such a repair can prevent transmission damage, cooling system problems and save starter and alternators. 



Leaking batteries should be replaced and are often under warranty

Simply cleaning a corroded terminal is usually temporary at best

Poor cables can create transient grounds

Poor grounds can cause electrolysis, damage transmissions, radiators and even engines

Poor connections can create very difficult electrical problems

Expensive battery harnesses can be repaired to better than new condition

Don’t let damaged cables cause major problems. AGCO stocks cable and terminals for all applications and can even build custom cables for you. AGCO, it’s the place to go!

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