The black on the outside doesn't hurt. You don't want that on the battery post or cable clamp where they make contact. That is a sign of oxidation. The post and clamp should be shined up with sandpaper or a wire brush, then immediately assembled and tightened. The thin stamped steel clamps typically used on import cars will bend to fit the post. If your replacement cable has the much stronger lead cable clamps, those are best cleaned with a battery post and clamp cleaner that has tapered cutters that match the taper of the battery posts.
Once they're assembled you can use some spray-on battery cable protector to prevent the oxidation but there are some things you have to be aware of. Those coatings are an insulator. If there is a gap between the battery post and a cable clamp that is not shaped properly, that is where that black oxidation will occur, and that is where the spray coatings will seep in. It can work its way around and make a poor connection even worse. You can also get those "juicy rings" that go on the battery posts first but again the juice will squish out and can get forced between the clamp and post creating a worse connection.
The advertising for those rings and coatings claims to neutralize the corrosion that can build up on battery cables. While it's true they will do that, there is more to the story. As a battery ages lead flakes off the plates and collects in the bottom of the case. That leaves less on the plates to absorb the current coming in from the generator to recharge the battery. The little remaining lead takes all that current so it starts to get hot. That makes the acid bubble, and those bubbles reach the underside of the top of the battery case. There the acid collects and starts to seep through the joint between the posts and cover. THAT is what causes the white powdery corrosion that looks like cauliflower. While those rings and coatings will try to neutralize some of that acid, experience has shown over and over that when that corrosion first appears the battery is going to fail within the next six months. There is nothing you can do to prevent a cell from shorting due to that flaked-off lead building up in the bottom of the case until it touches the plates, and those protective coatings aren't going to solve anything.
To say it a different way, if the battery is NOT about to fail, there is no need for those coatings because there will be no corrosion.
Saturday, April 13th, 2013 AT 1:46 AM