What does an "expired" battery mean?

The meaning of expired for batteries is different from the expired used when talking about food products. When a battery is expired, it means that the battery's manufacturer can no longer guarantee that the battery has a full life or charge. More specifically battery expiration dates are based upon when the battery's total self-discharge will exceed 20%.

What is a self discharge rate?

A batteries self-discharge rate is the speed at which a battery loses charge while sitting idle. Many people assume that batteries remain fully charged until they are used, but in reality, batteries begin losing charge directly after they are manufactured. The rate of discharge varies between battery type and brand and can even be affected by the temperature at which the batteries are stored. For a more in-depth look at the differences in self discharge rates visit our guide to battery chemistry or read table 2A below.

Where do I find my battery's expiration date?

The location of the expiration date varies depending on the type of battery and the packaging that is used. In the case of button cell batteries, many of them will have it on their box or plastic packaging, but will almost never actually be on the battery itself. Most batteries will have the date printed on each individual battery near the chemical composition or battery type information. Most times it will be easily visible and often is highlighted and separated from other text by a colored boxed area or some other distinguishing feature.

What is the shelf life of my batteries?

"Shelf life" refers to how long batteries will hold their charge without use, specifically for non-rechargeable chemistries. In terms of rechargeable batteries, shelf life refers to how long the battery can sit before needing a charge or expiring. Shelf life of batteries largely depends on the size, chemistry, and manufacturer. Our guide to battery chemistry provides a rough estimate of shelf life for each chemistry. For more accurate information you can check out the links below for specific manufacturers.

• Energizer Shelf Life
• Rayovac Shelf Life
• Panasonic Shelf Life
• Duracell Shelf Life (pg. 9)

What storage factors affect the performance/expiration date of my battery?

Batteries should be stored at a cool temperature as any high heat environment will accelerate the self-discharge process. However, storing a battery in a temperature that is too cold can also adversely affect the chemical components within the battery. Optimal temperature ranges for batteries vary depending on chemistry and brand but most batteries are suggested for 15°C storage, also known as room temperature. For a comprehensive look at battery temperatures visit the guide to battery chemistry or read through table 1A below.

It is not good to store batteries out of the package, whether carried loosely in a purse or jumbled in a junk drawer. Keeping opened batteries with other metal objects like coins, keys, paper clips, nails, can lead to potential short-circuiting of the batteries which will raise temperatures and put the batteries at a greater risk of leakage. Also keeping a "battery bin" for mixing and matching leftover batteries is a bad idea as using batteries of different capacities in the same device can lead to leakage through overworking of the weaker battery.