Question

Batteries don’t run forever. Why do you think batteries run down?

Answer 1

Because there is no such thing as immortal batteries.

When a battery is connected to a circuit, the charge moves through the circuit, and a chemical reaction occurs inside that separate the charges. The strength of this reaction diminishes over time and the battery eventually dies.

Answer 2

Answer;

Each charge cycle degrades the electrodes just a little bit more, meaning the battery loses performance over time, which is why even rechargeable batteries don't keep on working forever. Over the course of several charge and discharge cycles, the shape of the battery's crystals becomes less ordered.