Why do batteries lose charge when they’re not being used?

Question

Why do batteries lose charge when they’re not being used?

In: 2655

Answer 1

In most batteries there is something internally that separates the positive part and the negative part (separator). The separator is not perfect, and causes the battery to internally discharge itself. You can think of it as an extremely tiny internal short.

Modern li-ion batteries self discharge is extremely small, but it is there.

Pretty much anything else people are talking about isn’t self discharge, it’s degradation of the battery, which reduces capacity.

Edit: To expand some more, when you connect a battery to something, like a lightbulb, electrons flow from the negative part of the battery, through the light bulb, then to the positive part of the battery. In self discharge electrons flow from the negative part of the battery to the positive part through the internal separator.