Originally Posted by smokindave

Just because you don't understand the term doesn't mean everyone else is ignorant. As you read this (and you may not but, others will) try to picture all the parts on your bike that have a steel to aluminum interface i.e.; motor mounts to aluminum engine are just one.

Picture a dry cell battery. It provides electricity and eventually it will eventually run down. The battery consists of two different metals: the shell including the negative pole is made of one metal. The rod is made of a different metal and is attached to the positive pole In between the rod and the shell is a conductive gel or glop. For the battery to provide electricity (for you to use it), you have to connect wires that provide a metallic path from negative to positive that electrons can follow.

So, what happens is positively charged ions of metal dissolve into solution from the positive pole and migrate through the glop and reach the shell. Meanwhile (if the battery powered device is turned on), electrons travel through the wire from the negative pole to the positive. The positively charged ions meet the electrons, which reduce the metal back to metallic state. At some point all the metal from the rod dissolves, or the shell gets completely coated with metal from the rod, so there is now only one metal exposed instead of two, and the battery is "dead".

Dissimilar metals in a device can comprise a battery whether we want them to or not. If you have two different metals, and they are sitting in salt water or another conductor, you've got a battery. If you now provide a metallic path between the two metals (either a piece of wire or just bolting them together), the battery is "running", i.e., one of the metals is corroding.