Most battery manufacturers print expiration dates on their packaging. They also talk about things like self-discharge and shelf life. All of these things make a difference when you are choosing batteries for your electronic devices. But if you don’t know what the terms mean, they will not help you.
This post is intended as an introductory guide to everything you need to know about battery discharge and expiration. There is a lot more to learn, but the information presented here should at least give you a basic understanding of how to apply expiration dates to your battery purchases.
Our discussion will start with expiration dates. We do not apply such dates the same way to both batteries and food products. In terms of the latter, expiration dates are nothing more than a measurement of when food products offer the best quality. After the expiration date, quality begins to decline.
Expiration dates on battery packages serve a completely different purpose. They establish a clear point in time at which a manufacturer can no longer guarantee their battery will hold a charge. As a general rule, manufacturers calculate expiration dates based on when self-discharge is likely to exceed 20%.
Self-discharge is the next thing you need to know about. First, batteries do not literally store electricity. They generate electricity through an internal chemical reaction. Unfortunately, it is not possible to completely prevent that reaction from taking place spontaneously. It begins the moment a battery is fully charged. It results in what the industry refers to as self-discharge.
As a general rule, disposable alkaline batteries tend to self-discharge at a rate of about 3% per year. That is not bad. NiCad batteries tend to self-discharge as much as 15% during the first 24 hours and then up to 15% per month thereafter. Lithium-ion batteries generally self-discharge at 5% in the first 24 hours and then up to 2% per month from there.
Salt Lake City’s Pale Blue Earth says that it is best to prevent rechargeable lithium-ion batteries from fully discharging. They work best if they are not allowed to discharge below 20%. Thus, it is a good idea to recharge lithium-ion batteries after each use.
Battery Shelf Life
Battery shelf life is defined differently depending on whether you are talking about alkaline or rechargeable batteries. The shelf life of an alkaline battery describes the amount of time the battery will hold its charge without being used. The shelf life of a rechargeable battery is defined by the amount of time the battery can go without requiring recharging.
Alkaline batteries have the longest shelf life (7 to 10 years) simply because they self-discharge so slowly. Lithium-ion batteries have a very good shelf life as well. As for NiCad and NIMH batteries, they offer the shortest shelf life of all consumer batteries used in modern electronic devices.
Discharge During Use
One last thing to note is battery discharge during use. Disposable alkaline batteries discharge at a very steady rate. That is why you get consistent performance without a lot of battery fade. The same is true for lithium-ion cells. Discharge consistency is one of their many strong points.
NiCad and NiMH batteries discharge less consistently during use. They start out strong but then fade as they go. They also tend to offer less voltage across the board, making them less than ideal for high-voltage applications – like digital photography.
You should now have a basic understanding of battery discharge and expiration. Use what you have learned here to make better decisions regarding future battery purchases.