How should you treat your rechargeable batteries?
I always thought that the way you should treat your rechargeable batteries should depend on the type of battery that you are using. I thought that Nickel-Metal Hydride and Nickel-Cadmium rechargeable batteries should be completely drained down before reusing. On the other hand, Lithium Ion should never be drained all the way because that might cause them to lose polarity. Plus, Lithium Ion does not suffer from memory problems like the other rechargeable batteries.
Now, I am not the only one who thinks this. This article on batteries also says that Nickel-Metal Hydride and Nickel-Cadmium rechargeable batteries should be completely drained down before reusing.
Recently though, I have come across information that makes me think that I am mistaken, and that by draining my Nickel Cad batteries all the way down I have actually been shorting their life.
The start of my confusion came from this post from On the Level….
It turns out that you can ruin a rechargeable battery by running it down to zero. The polarity of the battery cells can even become reversed, ruining the battery for future charges.
Now I was going to leave a comment saying that this was only true for Lithium batteries. But before I did that I wanted to find an official source to quote. This is from the Dewalt FAQ on batteries…
Is it better for DEWALT batteries to be completely discharged before charging?
No. Just the opposite, you should stop using a battery as soon as you feel a substantial decrease in power from the tool. Completely running down a battery may damage the battery. Do not tape trigger to run down the battery.
That was a bit of shocker to me. Surely DeWalt still sells Nickel Cad batteries. To double check I went over to the Skil site and found this….
• Never fully discharge a battery! Do not fully discharge batteries by taping the trigger in the on position or by leaving work lights on.
• Recharge a battery when a tool is no longer able to complete the current application.
At this point I was confused. What ever happened to Nickel Cad memory effect? So I looked up Nickel Cad batteries on Wikipedia and here is what I found….
It is sometimes claimed that NiCd batteries suffer from a so-called “memory effect” if they are recharged before they have been fully discharged. The apparent symptom is that the battery “remembers” the point in its charge cycle where recharging began and during subsequent use suffers a sudden drop in voltage at that point, as if the battery had been discharged. The capacity of the battery is not actually reduced substantially. Some electronics designed to be powered by NiCds are able to withstand this reduced voltage long enough for the voltage to return to normal. However, if the device is unable to operate through this period of decreased voltage, the device will be unable to get as much energy out of the battery, and for all practical purposes, the battery has a reduced capacity.
There is controversy about whether the memory effect actually exists, or whether it is as serious a problem as is sometimes believed. Some critics claim it is used to promote competing NiMH batteries, which apparently suffer this effect to a lesser extent. Many nickel-cadmium battery manufacturers either deny the effect exists or are silent on the matter.
The memory effect story originated from orbiting satellites, where they were typically charging for twelve hours out of twenty-four for several years. After this time, it was found that the capacities of the batteries had declined significantly, but were still perfectly fit for use. It is thought unlikely that this precise repetitive charging (e.g. 1000 charges / discharges with less than 2% variability) would ever be reproduced by consumers using electrical goods.
An effect with similar symptoms to the memory effect is the so-called voltage depression or lazy battery effect. (Some people use this term as a synonym for “memory effect”) This results from repeated overcharging; the symptom is that the battery appears to be fully charged but discharges quickly after only a brief period of operation. Sometimes, much of the lost capacity can be recovered by a few deep discharge cycles, a function often provided by automatic NiCd battery chargers. However, this process may reduce the shelf life of the battery.[5] If treated well, a NiCd battery can last for 1000 cycles or more before its capacity drops below half its original capacity.
I looked at some of the sources quoted by the Wikipedia article. One of them was a technical manual from a manufacture of a Nickel Cad battery. It says….
Certain NiCd cylindrical cells employing sintered type electrodes experience memory effect. The memory effect occurs due to the possibility of alloying reaction between cadmium and nickel in the cadmium electrode. However, memory effect can be eliminated if cells are completely discharged. NiCd cell employing pasted electrode technology is much less susceptible to memory effect, because less nickel is present in the cadmium electrode.
So I guess I can call this a kind of vindication. But this same technical manual (and other documents on Nickel Cad) says that a complete discharge runs the risk of reversing the polarity of some of the cells so you should not do it. So even if completely discharging the battery protects from the memory problem, you will be losing cells by completely discharging the battery.
And this essay called Dan’s Quick Guide to Memory Effect; mocks those of us who believe in the memory problem. He says…..
True memory only happens in sintered plate NiCd cells (which aren’t necessarily the sort of NiCd you’re using, and are of course completely different from any kind of NiMH cell), and it only happens when you precisely discharge a cell to exactly the same level over and over again, and recharge it without any overcharge. True memory effect happens in satellite power systems, electronics test labs, and practically nowhere else.
As I said in the beginning, you can find other people on the web who disagree. But what Dan says agrees with what the manufacturers say. So I guess I am going to have to admit that I have been shortening the life of my Nickel Cad’s by draining them completely.
That is what you get for acquiring your knowledge of batteries from the old hands on the building site.