Rechargeable Battery Basics: Long-Term Storage

By: Anna Woodward

You know when you buy food that it will go bad at some point. Luckily, they print these expiration date labels on food and other products to let you know. You also know that there are places where food items should or should not be stored. But, did you know that batteries function in exactly the same way?

Just like food products, these mini power cells are perishable. That means that from the moment they are made, they begin to slowly deteriorate. Don't worry though, there are ways to keep and store those mini power cells. Here's what you should do to ensure the battery's long life.

The best temperature to store a rechargeable battery is around 60 degrees Fahrenheit. As they sit around, they start to lose some of their charge. This is called self-discharge, and it refers to the battery losing capacity without being used. Different types of power cells have different self-discharge rates. The ones containing nickel discharge fastest. This means that any Nickel-Metal Hydrate or Nickel-Cadmium rechargeable battery will self-discharge slightly faster than other types.

You might have heard that it is a good idea to keep your batteries in the refrigerator. This is the case only sometimes. If you live in a moderate environment, where your average room temperature will always be about 60 degrees, there is no need to refrigerate them. It will extend their life very, very slightly, and isn't really worth the trouble.

Refrigeration is suggested if:

- You live in a very hot environment. Even if stored at 85 degrees, a battery will only lose about 1/20th of its life in one year. If stored in 100 degree temperatures, it will lose more like 1/4th per year.

- You are storing Nickel Cadmium (NiCd) or Nickel-Metal Hydrate (NiMH) power cells. These will lose some of their capacity every day if not stored in the refrigerator or environments at 70 degree room temperature. If you can keep them where it's cooler than that, you may not have a problem.

If you do refrigerate your batteries, it helps them work better if you keep them in room temperature for a while before using them.

An acid based battery should be stored at full charge. Nickel and Lithium based power cells should be stored at half charge, or 40% charge. This will help keep them from using capacity over time, and you will see a better performance from them when you do use them.

Does it seem like your getting hit with lots of info all at once? Battery technology isn't easy to understand, so let's break it down a little. Here is a summary of some basic guidelines to follow:

- The best place to store batteries is in a cool, dry place. If your average room temperature is over 60 degrees and you need long-term storage, or if you are using lithium or nickel based power cells, keep them in the refrigerator. Then, bring them up to room temperature before use. Never keep any kind of power cell in the freezer.

- Store the nickel and lithium based rechargeable battery at about half their charge. Storing them at full charge will drastically shorten their life. It depends on the specific battery type, but in general about half charged or 40% charged is good. Also, don't store lithium batteries that have no charge. If it is down to 0, charge it a little bit before you store it.

- Lithium batteries don't keep as well as other types, so buy them as you need them. It's okay to store an extra to have on hand, but it's not worth it to buy a bunch and store until you need them. By that time, there won't be much charge left.

- For heavy duty, lead based power cells, follow the instruction manuals carefully. They will give guidelines for storage including when to periodically charge them and under what conditions they should be stored.

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