Batteries ?

Question

why does batteries have an expiration date? any kinda of battery but car has an experation date

Answer 1

Even a car battery has an expiration date.  They're usually guaranteed for 5 years.  But any battery is powered by chemical reactions inside the case.  Eventually the chemicals lose their ability to react for various reasons.  For a non-rechargeable battery, the chemicals slowly react even when they're not connected to anything.  The 9 year shelf life for a standard alkaline battery is actually pretty impressive.  For rechargeable batteries, the chemicals slowly react with other things, the case of the battery, Oxygen that very slowly leaks in.  The slow leak out of gases that rob the battery of it's reactive chemicals.