There is always black stuff on my battery negative, what is it?

[illitirit]

After using my batteries day by day, there is always buildup of black stuff on the bottom of the battery (negative). I was just curious what it is and is there anyway to prevent this from happening.

I clean it all the time, but it has left a permanent ring in all my batteries (VTC5x6).

Here is a pic

 

[sedge]

Deoxit Gold decreases that occurance.

 

[Baditude]

Carbon buildup. Use isopropal alcohol to clean the contacts and battery. You can also use a pencil eraser.