Duracell PowerCheck - How Does It Work?

Question

I've been using these batteries for a long time and I've never seen such a feature.

There's a band on its outer wrapping having two ends: The white circle on the left side and the another one on the right side (not visible because it's under my thumb):

If you press hard on those ends, a bar slowly fills up and shows the current capacity of the battery:

This one is a brand new battery, so it shows full.

I didn't even try Googling because of the risk of hitting a lot of fake information (I don't know why but I feel so). Anyway, I trust here, so I asked here.

Any ideas?

Interesting. I'm 32 years old and maybe I saw one but couldn't remember now. An interesting and useful feature anyway. — Rohat Kılıç, May 18 '17 at 07:51
A better question is WHY rather than how: because it wastes energy when you use this feature. — , May 18 '17 at 20:32
@nocomprende Why not? The feature is useful to the great majority of people, who don't have a multimeter. It presumably doesn't consume any power when it's not being used, and using it occasionally presumably doesn't consume any significant fraction of the stored energy. — David Richerby, May 18 '17 at 22:08
Next time, try Googling first, I googled the title of your post "Duracell PowerCheck - How Does It Work", and the top 5 results were reasonable explanations of how it works, including 2 pages from Duracell itself. — Johnny, May 19 '17 at 00:08
@DavidRicherby multimeter is not that useful for testing batteries. The idea is that they last as long as they last, and this kind of testing only furthers the agenda of the manufacturer. If you are concerned about running out, keep more on hand. We don't need a spurious "feature" which amounts to pouring some milk on the ground to see how full the bottle is. We can be adults and take responsibility instead. — , May 19 '17 at 12:45
@nocomprende Checking a batteries capacity makes you not an adult and irresponsible? Overreacting much? — DasBeasto, May 19 '17 at 13:02
@Johnny Yeah, you are right. I thought so, after I first read Arsenal's answer below. But you see that how much people fav'd and rated this question and the answer? I mean, doesn't this mean that it's a good thing to ask here too to share the info with other people? If I googled first, nearly 100 people wouldn't have such a valuable info. — Rohat Kılıç, May 19 '17 at 14:26
@DasBeasto test away. But I don't need extra gadgets added to my batteries whose main purpose is to get me to buy more. I can cope with managing my battery supply with no help from the corporation. Primary cells are discarded. Why would we add more throw-away stuff to them? This seems irresponsible to me. Besides, the heat released in the testing process contributes to Global Warming. Doesn't that keep you awake at night? — , May 19 '17 at 15:05
@nocomprende You've piqued my curiosity. Now I want to buy one of these and put an ammeter on the gauge to see how much power it actually wastes, and use my IR camera to see how hot it gets. Duracell thanks you for helping sell their batteries :) — Doktor J, May 19 '17 at 16:48
@DoktorJ I am a good Capitalist. No, Environmentalist. Now I am confused, which to support? :) — , May 19 '17 at 16:50
@BaileyS as stated in the answer below, the tester draws about a half amp of current, which is pretty significant for a AA cell. Enough "checks" would deplete it. I was going to include a proof, but this comment field is too small to contain it. — , May 19 '17 at 19:54
@BaileyS that's fine. Far be it from me to say the built-in tester was a conspiracy. I retract my statements. I am just so used to products, 'features', advertisements and everything else about the commercial world being self-serving that I figure that is what it must be. I do not understand competition, sports, status, comparison, getting ahead, making it big, profit, etc. Makes no sense to me. Just do something useful and enjoy life. We don't need 20 companies making batteries: one good supplier would be enough. — , May 20 '17 at 20:43

Arsenal · Accepted Answer · 2017-05-19T21:11:28.543

96

According to the German Duracell website:

As you press the points, a current will flow through a metal strip getting warm. The display is a thermochromatic one. So the increased temperature will result in a change of color from black to yellow or red in your case.

The strip has to be designed in a way so that the heating of the single elements corresponds to the state of charge. So at the bottom it will have a small cross section and at the top it will be a wider cross section, so that only a full battery will give enough current to heat the upper part enough to cause the color change.

This also explains why it isn't always on. It would drain the battery.

So this seems to be a question and answer with a lot of attention, so I went off to our old battery storage and picked up a Duracell AAA with powercheck feature and disassembled it.

Measuring the resistance of the whole strip wasn't as easy as I thought, but I got the most stable result with a reading somewhere between 2 and 3 Ohms. So it's quite close to a short circuit. Considering the internal resistance is really low at the beginning, you have around 0.75 W wasted to indicate the state of charge. (Around 560 mA with 1.4V and 2.5 Ohm)

The AAA battery would be dead in an hour.

So this is what it looks like:

The naked cell: Nearly all of the body is made up of a cylinder connected to the + side, a paper barrier and a metal plate connected to the - side.

The wrapping: Has another paper separator, providing space between + contact and the cylinder. The red stuff is some sort of insulation coating. And of course you have two metal contacts, one for + and three smaller ones for -.

And below the coating we can make out the metal structure: the metal is still behind a cover of some blueish (teal?) coating. But as predicted, you see that the track is rather narrow at the bottom of the scale and gets wider to the top of the scale.

Thinking a bit more about the paper separator on the wrapping and the long cutout lead me to the following conclusion: The long cutout provides an air cushion below the metal strip acting as a heat insulation. Probably even the paper would have enough heat conductivity to cool the strip significantly, maybe it wouldn't even work.

edited May 19 '17 at 21:11

answered May 18 '17 at 06:51

Arsenal

17,464
1
32
59

I checked [the English website](https://www.duracell.co.uk/get-the-most-from-duracell-batteries/) but only watched the video. It showed me nothing useful, though. Now I noticed that the first paragraph on the page explains roughly. Thanks for showing. – Rohat Kılıç May 18 '17 at 07:55
7

This is what the label [looks like from the inside](http://i.ucrazy.ru/files/i/2012.1.11/83276137_002.jpg). – KlaymenDK May 18 '17 at 09:10
7

Also note that if you press it hard enough, you actually change the meter by adding your body heat to it. I used to play with these meters when I was little :D – John Hamilton May 18 '17 at 09:37
the photo of the chromatic gradient makes it look more like a red bar graph than to the eye. I wonder if coherent or rather polarized light makes a difference. Effectively it is an ammeter with about 1Watt or so peak? – Tony Stewart EE75 May 18 '17 at 13:58
2

@KlaymenDK I disassembled one on my own and took pictures. – Arsenal May 18 '17 at 14:59
2

@Arsenal Wow! Awesome! Danke schön! – Rohat Kılıç May 18 '17 at 15:04
1

I wonder how accurate that is at varying ambient temps. Well, probably accurate enough to say "DEAD" or "NOT DEAD" battery. – Wesley Lee May 18 '17 at 15:07
6

@WesleyLee the whole thing is very dependent on ambient temperature, it tells you on the label to test at 21 °C. Don't know how accurate the thing is even under best conditions. Under warm conditions the battery will be indicated as more full. Probably even more enhanced as the internal resistance will drop as well under those conditions, allowing a bit more current to flow heating even more. – Arsenal May 18 '17 at 15:11
Yeah I mean, it probably isn't reliable at all at 35ºC or 0ºC, most people wouldn't know that. – Wesley Lee May 18 '17 at 15:13
Note that this is really telling you "how much current it can deliver under a [given] load" - which is different than "how much charge is left in the battery". It is a somewhat decent *approximation* of charge left, though this part of the graph is somewhat "flat" during the "useful" life/area of the battery. This means while you can tell if the battery appears to be "good" right now - it gives you little idea of how much charge is LEFT. Gauging actual battery charge is a MUCH more complex subject than this little metal strip ;-) – Brad May 18 '17 at 18:16
2

The whole point was to **get you to buy more batteries**, by buying them, then by wasting the battery's energy determining when you have to buy more. It is the closest thing to a perfect product scam I have seen. – May 18 '17 at 20:30
1

I remember when they used to build one of those into each blister pack instead of building one into each battery. It probably cost them less that way, but the down side was that devious consumers could use it to test batteries made by that _other_ company. (Don't ask me how I know!) – Solomon Slow May 18 '17 at 21:16
1

@jameslarge you are going to destroy the Capitalist system! What is*wrong* with people like you!? – May 19 '17 at 12:51

Duracell PowerCheck - How Does It Work?

1 Answers1