Eli5: Why do small batteries sometimes need their seemingly clean contacts wiped clean in order to work in a device?

Question

Eli5: Why do small batteries sometimes need their seemingly clean contacts wiped clean in order to work in a device?

In: 19

Answer 1

So as you’ve already concluded: corrosion is the main factor. Contaminants are another. Smaller batteries with bad contacts are often held together by friction. One or two springs keep the battery in place. Spring wants to extend creating a force lateral to the battery this in turn creates a higher friction perpendicular to the battery. This creates more corrosion.

Now this is all well and good but this is just one aspect because just minor corrosion doesn’t reduce conductivity. Small batteries also tend to be used in small appliances that tend to be jostled around. This jostling allows air to occasionally interrupt the contacts but do to the voltage it might create tiny sparks. These sparks also create corrosion, at a much larger scale as it also promotes oxidation of the contact points. A very small layer of “rust” can significantly reduce conductivity.

When a battery becomes old, some might also leak acid (that white crap on your electrical christmas decorations when you forgot to take the battery out). Acid is highly corrosive and if not in an aqueous solution a pretty bad conductor.