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

In addition to oils from your hands, there can be a thin layer of corrosion or oxidation on the batteries. In addition, some new coin batteries have a bitter coating to prevent children from eating them that can interfere with some devices.