[T3] Battery cables

Jim Adney jadney at VWType3.org
Wed Dec 2 18:44:25 PST 2015

On 2 Dec 2015 at 16:47, Soren Jacobsen wrote:

> When I cut the old one apart, the reason for failure was clear:
> corrosion in the connection between the clamp and the wire strands. 

The real enemy here is acid attack. This is most common after a 
battery has been mistreated by hammering the clamp down on the post. 
Unfortunately, this practice is almost universal in shops that 
install batteries. 

The problem is that the shock of hammering breaks the fragile 
ultrasonic weld between the post and the plastic case. The damage is 
invisible, but the result is that acid can wick up onto the 
post/clamp and attack the copper wire.  

When this happens, most people will try to clean off the corrosion, 
not realizing that the film of acid is still there and is replenished 
every day. There's no way to repair the battery; nothing will stick 
to the polyethelene. I had a friend who tried to fix his problem with 
layers of very carefully applied epoxy. It was good epoxy and he 
cleaned the surfaces well before applying it, but it did no good.

I suspect that the various cures sold to prevent terminal corrosion, 
like the red/green felt washers and special sprays, will slow down 
the process, but eventually they give out and the attack continues. 
In our cars, where the battery is really out of sight, there's little 
chance of noticing a problem before it's too late.

Note also that this is an especially bad problem with modern cars 
where the battery clamps are made of thin wrap-around strips of 
copper. Those corrode MUCH faster than the cast lead fittings of 

[And don't get me started on the clamps that you pinch onto the cut 
off ends of your old cable. Those lose good conductivity in about 1 
year, tops.]

I'm afraid the only solution is to replace the battery and install it 
carefully yourself.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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