My *nix world

Recharging alkaline batteries

"Most alkaline batteries available are disposable, designed to be used until exhausted, then discarded." (source Wikipedia).

That's probably true. The most of us just throw these batteries to the disposal bin because we believe they are not rechargeable. We believe what is told without having doubts, right?

battery

Wrong! Sometimes it would be better if we would ask questions or if we doubt what is told.

The truth (proved by experiments) is that they can be recharged. Most likely they have a threshold that dictates how many times they can be recharged or how long a recharged battery will long.

Motivation

If you really want to save money, if you care about your children and your grandchildren future then you can do more than just recycling these batteries. By using ten times the same battery you save not only money but you also contribute in reducing by at least ten times the recycling and the manufacturing process, processes whose direct result is pollution.

Recharging alkaline batteries

I have a bicycle headlight that uses 2 x 1.5V batteries. As I'm riding the bike at night the batteries discharge quite frequently. The idea is to try to recharge them as often as possible without buying a new set (see Motivation).

To reuse them you have to recharge them. Although they are not supposed to be recharged you can do this if you know what you are doing. I have build a 5W solar panel that costed me only five bucks. I use this solar panel to recharge these batteries so that I reduced the pollution maximum possible (when you use electric power - eg. to recharge your batteries - you contribute to the global warming, although less than when you re-buy a new set of batteries). This setup is ideal but if this seems to you somewhat cumbersome then you can buy a battery recharger that does the same thing.

A simple 1A @ 5V battery charging board would cost you only 1 USD (on eBay):

recharger

The experiment

The experiment I've done was to take two dead alkaline batteries and recharge them. Although I am using usually my solar panel to recharge my batteries, in the following experiment I've used the charging board above just to make the setup as simple as possible.

As you will see in the video clips below when the batteries were dead their voltage was around 1V without no chance to light the bicycle headlamp bulb. After charging them they got 1.7V and the bulb lit successfully as the batteries were new.

Let's see the experiment:

What I've done was to link two "fully" discharged 1.5V AA batteries in series and to connect this circuit to the charger circuit board mentioned earlier. As you will see in the video clip below they were measured and shown ~1V each. That means they were discharged. I powered the battery charger and let it to charge the batteries for about 75 minutes.

Then 75 minutes later:

I disconnected the batteries from the charger and then I measured again their voltage. Now it shows 1.7V (be carefully not to exceed the 1.5V; depending by the battery type/manufacturer it could be safe to go just a little more; 1.7V was fine with me). It was just enough loaded to light my bicycle headlamp again.

I do the same with all the batteries that I use in a flashlight, remote-control, etc. It just work!

What's really happening at atomic level

The battery consists of two different chemical where one has an excess of electrons while the other one has a deficit of electrons. Let's assume that the negative end of the battery is called cathode and the positive end of the battery is called anode.The cathode is negative because the substance (chemical element) that it .... has an excess of electrons. The anode is positive because the chemical substance .... has a deficit of electrons.

The normal/natural state of a chemical element is the state of equilibrium where its number of positive and negative charges are equal. Our cathode is negatively loaded but it wants to be in equilibrium. The same happens with the anode which has a deficiency in electrons (i.e. has more positive charges than negative) which also wants to be in equilibrium. The positive charge is represented by the heavy particle called proton (that little particle that among neutron forms the atom nucleus) while the negative charge is represented by this very tiny particle called electron. In order to establish the equilibrium state some negative charges have to flow to the positive charges or vice-versa. There is a saying that says "if the mountain will not come to the prophet, the prophet will go to the mountain". Who do you think that will move to who: the electron to the proton or the proton to the electron? Well, it is always the lightweights (like the prophet) one and never the the heaviest one (like the mountain).

So in order to establish the state of equilibrium the electrons have to flow from the cathode towards anode. Inside the battery that's not possible because the two (anode and cathode) are isolated from each other.

When you connect the battery's anode and cathode ends to a lighting bulb (for example) the electrons will start to flow through this circuit (also through bulb filament) from cathode towards anode. Because in their way the electrons hit the atoms of the bulb filament they "rub" those atoms which in turn start heating (just try to rub your palms, you will see the immediate effect). The more electrons travels through filament the higher its temperature will be. When the temperature is high enough it will start be incandescent and it will radiate light. It doesn't mean that those electrons were consumed, no! They just flew from cathode through bulb filament to anode. Finally they are "home", the state of equilibrium has been reached. When there is a state of equilibrium there is no excess of electrons and thus there is nothing available to flow from cathode to anode. We call this "the battery is dead".

So in order to bring the battery to life we have to change this equilibrium state, we have to take some electrons from the anode and move them back to the cathode. But how can we force them to do that because it's somehow against their nature, against their equilibrium/natural state? Well, if we use enough force we can push them away from the anode to the cathode so that the anode will have again a deficiency of electrons while the cathode will gain these electrons and thus will get a surplus of electrons. Where does that force come from? Well, it could be from sun (if we use a solar panel) or from your power grid (if you use a electrical battery charger). Anyway, it comes from somewhere because nothing is free.

The question is: is this process possible with the alkaline batteries? Well, it depends on the chemical materials used in the battery. The chemical reaction (that allows the electron to flow back from cathode to anode) is reversible with some materials and with some materials it's not. Also, depending by the chemical materials used in the battery this process can be limited. Those rechargeable batteries use some chemical materials where this process is reversible and it can be done/undone several thousands times. In the case of alkaline batteries the chemical materials that are used allow you to reverse this process only a dozen times.

When it works

To better understand when it works you should consider the voltage as the pressure of air in a balloon and the amperage(the current) as the mass of air within the balloon.

To be able to inflate a balloon you have to blow air with a pressure larger than the pressure of the air that already exists in the balloon. The same applies here: to be able to "blow electrons in a battery" which have "a pressure" (i.e. voltage) of 1.2V you have to use a pressure (voltage) that is larger than 1.2V otherwise it will happen exactly the opposite: the electrons from your battery will flow into your "blowing device" (solar panel, battery charger, whatever). Like when you inflate a ball/balloon: if you use too much air the ball/balloon will finally explode. When you use a blowing device that has a very high pressure (in our case voltage) it is able to deliver a very large quantity of air (in our case electrons) per seconds so that the ball/balloon will reach quite quick the maximal supported amount of air (i.e. electrons). When this threshold is exceeded the balloon will explode. The same happens with the battery.

I hope that this analogy helped you to understand what's happening, why and when it works.

Conclusion

The alkaline "non-rechargeable" batteries are in fact rechargeable. There are, however, few considerations that I already explained earlier. Please read more here.

Warning

Don't try this at home unless you know what are doing. Note that if you "push" too much current into the battery it will firstly start to leak, boil then it might even explode. Although I don't believe you will die from this you never know what can happen. Have you heard the expression "sometimes shit happens" ?

Now, if you think that this article was interesting don't forget to rate it. It shows me that you care and thus I will continue write about these things.

 
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Recharging alkaline batteries

Eugen Mihailescu

Founder/programmer/one-man-show at Cubique Software
Always looking to learn more about *nix world, about the fundamental concepts of math, physics, electronics. I am also passionate about programming, database and systems administration. 16+ yrs experience in software development, designing enterprise systems, IT support and troubleshooting.
Recharging alkaline batteries

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