Why do Rechargable Batteries Lose Their Capacity to Held Energy?

[AFTT47]

The one I'm most familiar with is lead-acid, like a car battery. Like most battery types, they suffer from self-discharge. In their discharged state, the lead can sulfate and harden which destroys its ability to store energy. It is different for other battery types but in all cases, permanent chemical changes occur because of age and heat. In most cases, being left in a discharged state is a problem too as well as being drained to the point where it's nearly dead even for a short time.