The ground (black) terminal clamp on the battery in my 2007 Mazda-6 has become loose to the point that sometimes the start motor will drain the whole electrical system before it engages. At that point I have to pop the hood and shimmy the clamp to get a connection sufficient to start the car.

I have hit the limit tightening the clamp nut but I can still turn the clamp without much effort. (Maybe this is a consequence of differential metal shrinkage as temperatures have recently been below freezing?)

What is an expedient or proper fix for this? I don't see any corrosion on that terminal. My first inclination was to shim it with some copper wire between the clamp and the terminal, but for all I know that will cause galvanic corrosion.

Battery with loose black clamp

  • 1
    How old is your battery? If its 4+ years then it may be on the way out and due for replacement too. This may or may not fix the clamp problem.
    – Criggie
    Mar 4, 2019 at 18:56

3 Answers 3


If the clamp is no longer getting tight enough, that could mean the metal is stretched and possibly weak. A dealership would want to replace the whole ground cable with a new, molded on clamp. If there is any slack in the cable, you can buy a replacement clamp and put that on the wire. One way or another, new clamp is the "proper" fix.

In the mean time, there are also "terminal shims" that are made to be a quick fix for this problem at many auto-parts stores:

enter image description here

Lead post shim, random example

They are made out of lead so you don't have to worry about different metals reacting with each other.

  • Never seen those before.. I used to have the molds and re-cast the battery terminals, pouring the melt...
    – Solar Mike
    Mar 4, 2019 at 18:23

Replace it, with something like this:

enter image description here

  • That's an interesting wire attachment style. I like that the wire would come off at a 90 degree angle. I haven't seen this style in the US - maybe I haven't looked hard enough tho.
    – JPhi1618
    Mar 4, 2019 at 17:59
  • They were the style easily found in the UK - but there are many different styles now - clamps like that with wing nuts for cable terminals or studs and nuts etc
    – Solar Mike
    Mar 4, 2019 at 18:02
  • I also like that it has two holding screws on it ... nice add. Mar 4, 2019 at 18:12

My favorite is adding a "custom" shim...i.e. pounding a nail in there so it'll tighten up:

enter image description here

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