Letter to the Editor: The following was submitted in response to this article.

Great article with one exception, item #7 is incorrect. This is the way we thought of batteries 20 years ago, it is not true today. The number of charge cycles is dependent on the "Depth of Discharge" you are placing the battery under. A battery that is used 20 minutes per day and fully recharged after each use can go 1,500+ charge cycles over its life time where as a battery that is used 3 hours each day may experience a life of only 400 charge cycles.

Think of a battery in its true form, a box that holds energy. Over its life time, it is only able to supply a set amount of energy/power. Lets just use a fictitious number here for simplicity and say Battery X can supply 10,000 units of energy over its life time if it is maintained and charged properly. As the battery approached the end of life of 10,000 units, it becomes weaker and not able to hold/supply as much energy as it did when it was new and in its optimal performance period of its life. However, the same battery in various situations will perform for different periods of time and charge cycles. Lets look at two examples:

10,000 unit battery X used for 20 minutes per day taking 50 units of power each day, then is fully recharged each day before its next use. 10,000 / 50 = 2,000 charge cycles and could last for several years.

10,000 unit battery X used for 200 minutes per day taking 500 units of power each day, then is fully recharged each day before its next use. 10,000 / 500 = 200 charge cycles and could last less than a year.

There is NOT a limit to the number of charge cycles a battery can obtain. There is only a limit to the amount of power a battery can store/provide over its life time. A much better term for this is "Serviceable Life". This would be defined as the amount of power a battery can provide over its life time. We need to get away from the old charge cycle idea, it is no longer a true measure of a battery.

So at the end of the day, a battery is a battery, its only capable of supplying a set amount of power over its life. How quickly we consume that power determines the life of the battery, not how many times we charge it.

Another way to think of this. Think of a car tire, they have mileage ratings. For example a tire will say "40,000 mile warranty". So if I drive 10 miles a day I know that tire will last me quite a while. Whereas if I drive 100 miles a day I can expect that tire to last 1/10th the amount of time it would last if I only drove 10 miles per day. We don’t say that the tire will last 1,000 drives do we? Meaning once I drive my car 1,000 times with this tire no matter how far I drive the tire will need to be replace, right? Now apply that same idea to batteries and I think you can see the problem with what #7 is trying to apply.

Keith A. Essenyi
Current Product Manager, Commercial and Essentials
LEED Green Associate
Tennant Company