Battery Discharge Depth and Life Expectancy of Rechargeables

Rechargeable battery lifetimes are measured in cycles or how many times they can be discharged and recharged. Once a rechargeable battery cannot take a full charge any longer, you will know it, and chances are it is ready either for reconditioning or retirement. After using a rechargeable battery hundreds of times you will be able to tell if it is not “acting right”.

The “depth of discharge” has a critical effect on the life expectancy of a battery. Life expectancy of a rechargeable battery is measured in two ways. One is the ability to charge to full capacity, and the other is the number of cycles expected in the battery. When the capacity of a battery, or its runtime, begins to fade, it is an indicator that it needs attention. With NiMH batteries, very often reconditioning will bring it back to nearly full capacity life. You can think of reconditioning a battery much as “reformatting” it. Having a quality charger that reconditions your batteries is a great way to extend their use.

Reports tell us if a battery is normally discharged only 80% of its total capacity, it will last longer than one regularly discharged all the way down. Daily use and recharge is not as apt to bring about the “deep discharge” that comes from infrequent use and seldom charging. Batteries that are recharged frequently before they totally discharge, are reported to take 25% more cycles than those totally emptied before charging.

What does this mean? It is better to put the rechargeable batteries right on the charger after use instead of leaving them in the device to self-discharge. If the device is used daily, or even several times a week, there is no need to do anything except just charge them when they naturally run down. You can tell when cameras get slower in response, and radio devices start to get static, that the batteries need to be changed. The important feature about NiMH rechargeable batteries is the way they hold their strength almost all the way to empty. This is in contrast to alkaline batteries that start a slow, steady dropoff of voltage and capacity right away.

If batteries are kept inside a device in storage for long periods (more than a month), it is better to remove them and charge them up for the next time. Keeping a bit of life inside the battery before recharging it is better. A small bit of life in the battery makes it charge up more smoothly and keeps the power coming.

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