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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):

enter image description here

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

enter image description here

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?

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    \$\begingroup\$ Note that this has been around since the mid 90s \$\endgroup\$ – PlasmaHH May 18 '17 at 7:34
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    \$\begingroup\$ @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. \$\endgroup\$ – David Richerby May 18 '17 at 22:08
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    \$\begingroup\$ 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. \$\endgroup\$ – Johnny May 19 '17 at 0:08
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    \$\begingroup\$ @nocomprende Checking a batteries capacity makes you not an adult and irresponsible? Overreacting much? \$\endgroup\$ – DasBeasto May 19 '17 at 13:02
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    \$\begingroup\$ @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. \$\endgroup\$ – Rohat Kılıç May 19 '17 at 14:26
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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. Naked cell

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 -. wrapping of the battery

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.

Conductor of the indicator


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.

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    \$\begingroup\$ This is what the label looks like from the inside. \$\endgroup\$ – KlaymenDK May 18 '17 at 9:10
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    \$\begingroup\$ 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 \$\endgroup\$ – John Hamilton May 18 '17 at 9:37
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    \$\begingroup\$ @KlaymenDK I disassembled one on my own and took pictures. \$\endgroup\$ – Arsenal May 18 '17 at 14:59
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    \$\begingroup\$ @Arsenal Wow! Awesome! Danke schön! \$\endgroup\$ – Rohat Kılıç May 18 '17 at 15:04
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    \$\begingroup\$ @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. \$\endgroup\$ – Arsenal May 18 '17 at 15:11

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