So my positive cable post is black and corroded. I clean it nice and shiny and a week later same problem. It has been like this the whole 7 months i have had it.


1990 xj 4.0 automatic

 

Is the battery case cracked near the + terminal?

 

This is very possible! My brother had a crack battery case and when he went to change it out the battery sparked and caused the battery to explode in his face. So, Be careful when you check it out and if it is cracked change it out.

 

Also adding grease helps Conductivity as well as preventing corrosion

 

Check your at rest voltage. You might have a cell or cells going bad, causing a lot of outgassing.

 

Well that's not what i wanted to hear but i will check. Thank you

 

That's what we call an electrical system leak. Something is radiating electricity causing advanced stages of oxidation wich can be black, brush battery posts, change battery cable terminals to high quality ones, put the anti acid battery felt rings on, (always a good thing to do) if its coming from the battery then replace it. It CAN be somewhere like the alternator that's storing excess power and firing it back thru the system, this is extremely uncommon though. Don't just toss ur batt yet thou
It's holding power fully?

- Jeep certified mechanic

 

I've never heard of an alternator "storing" power.

 

They don't other than for a small fraction of a second while the magnetic field dissipates.

The black coating is either from severe overheating or exposure to Hydrogen gas. The first is easy to check for...you won't be able to touch the terminal. Cracks are actually somewhat common, the terminals are a stress point with little reinforcement. As the plastic case ages it gets weak.

 

This, or it is leaking right around the post.

 

i didn't find any cracks, it isn't overheating. it holds a charge for the most part even now and then i will have to get a jump but that is like once every 6 months.