Why don't batteries last forever?

Question

Why don't batteries last forever?

Answer 1

batteries work from chemicals reacting to produce electricity. When the chemicals are used up, the battery is dead.

They can't last forever for an additional reason, that that would be a perpetual motion machine, which is impossible.

Answer 2

The voltage difference across the two terminals of the battery is fueled by the chemical reaction of the materials, generally a metal and an acid, inside the battery.  When the metal becomes too corroded the reaction slows down and the battery gets weaker and eventually dies.