EEVblog #772 - How To Calculate Wasted Battery Capacity

[Pentium100]

I'd like to see constant current and constant power discharge curves down to zero volts. It would be interesting to see how much more energy a germanium (for example) based device can use. Or a device that uses two batteries in series, but cuts out at 0.8V.

However, I do not have the necessary equipment to do it.

[apis]

Would be interesting to see the temperature response, but that's not so easy to test I suppose.

[apis]

No matter how you look at it, Batteriser means a LOSS in overall power.

Yeah, that's my conclusion as well. The truth will come out eventually.

[Wytnucls]

First, Dave's calculation assumes that there is no energy available once the voltage under load reaches 0.8 volts.  Presumably, if we had a load with a dropout voltage lower than 0.8, we could draw a small amount of extra energy beyond what the calculation considers to be 100%  --- it's pretty clear that the discharge curve becomes close to vertical, however, so this extra energy is pretty much negligable.

This is why the manufactures usually don't provide curves below 0.8, it is the defacto industry standard dropout voltage at which point any extra energy in the battery is consider negligible. As I mentioned in the video, there is some energy left below 0.8V for really small currents, and this is why a joule thief can flash a LED down to bugger all. Very small amount of energy, very niche applications where it can be used.
I didn't want people thinking they should go to the ends of the earth to design products with a 0.5V cutout voltage, that's rarely done in the industry.

They claim their DC to DC converter works down to 0.6V, so perhaps it is worthwhile to investigate how much energy is actually available in that uncharted region.
My rough discharge test points to 60mW down to 30mW over a 5 hour period between 0.8V and 0.6V for a AA battery.

[HKJ]

I'd like to see constant current and constant power discharge curves down to zero volts. It would be interesting to see how much more energy a germanium (for example) based device can use. Or a device that uses two batteries in series, but cuts out at 0.8V.

However, I do not have the necessary equipment to do it.

I cannot do it to zero, but to 0.3 volt with 0.1 watt constant power:

All the spikes is because I pauses the discharge 1 minute every 10 minutes to see the unloaded voltage. I.e. my time scale is 10% to long.
If I had held a longer pause the cell would have recovered more voltage.

Here is a zoom of the last part of the above curve:

[HKJ]

I wonder why Dave want to do all that drawing on his curves to get remaining energy, why not directly make a curve showing it.

A normal discharge curve with 0.1A discharge:


Using energy scale:


Showing remaining energy (It is the wrong way, but my charting system want increasing scales):


At some other currents (0.2A, 0.5A and 1A):

[Dr. Frank]

Dave,

that could have been a nice educational video, but you really flunked it, sorry! 
As others already mentioned, you did not show the power integral area correctly, i.e. from 0.8 to the discharge line only, instead of zero volt to the discharge line.
That is really annoying, and may disturb students, for whom this video is intended for, obviously.

It could also have been very easy to bust the rest out of the residue energy myth, by discharging the battery to its very limits, below 0.8V, as these energy saver gadgets claim to operate well below that voltage.
 
It's a pity you missed that chance.

Frank

[Pentium100]

No matter how you look at it, Batteriser means a LOSS in overall power.

But what if you stick it on only after the device turns off because of low battery voltage?

[nitro2k01]

If there is no significant energy below 0.8V then you don't have to go to 0V. What I did was correct when you assume (as is industry standard practice to do) there is zero usable energy below 0.8V.
The numbers come out exactly the same regardless of whether you include all the way down to 0V or just down to 0.8V. Those who are unsure about this need only try it.

Well, you have a nice setup of a logging electronic load, so this would have been easy to prove empirically. Just keep loading the battery until at can no longer provide your x mA (or if you were doing a constant power measurement x mW.) If this point is 0.75 V instead of 0.8 V, then the numbers wouldn't come out exactly the same for a 0.8 V or a 0 V cutoff. I'm not saying this because it would necessarily be viable to use this last amount of energy, but because it would have been so easy to extract this data and get a true "0%" point for a certain load, and for a particular battery.

[jimon]

I'd like to see constant current and constant power discharge curves down to zero volts. It would be interesting to see how much more energy a germanium (for example) based device can use. Or a device that uses two batteries in series, but cuts out at 0.8V.

However, I do not have the necessary equipment to do it.

I cannot do it to zero, but to 0.3 volt with 0.1 watt constant power:

All the spikes is because I pauses the discharge 1 minute every 10 minutes to see the unloaded voltage. I.e. my time scale is 10% to long.
If I had held a longer pause the cell would have recovered more voltage.

Here is a zoom of the last part of the above curve:

Thank you ! Now I can rest because I know that after 0.8v point there are 1-2% of charge left

[dcac]

No matter how you look at it, Batteriser means a LOSS in overall power.

But what if you stick it on only after the device turns off because of low battery voltage?

Yeah there's no question as long as the battery by it self has enough voltage to power the device Batteriser will simply be drawing/wasting extra energy.

But BR claims: "Works on all new and most "used" batteries." so this suggest it can/should be used with new (unused) batteries.

But then again the BR Apple keyboard video shows it being used after battery status indicates Low level.

[RobEE]

Dave,
This video was very informative, as always, but the videos where you talk while doing screen capture of your computer screen can be a little boring. Have you ever considered setting up a camera and recording yourself while you talk? Then you can do either a picture in picture shot where your talking head is in the corner of the screen, or you can cut back and forth between you and your computer screen. Doing either of those, or a combination, would make your screen capture videos more entertaining. Sorry if this has already been brought up before, but I don't spend much time on the forums. Keep up the great work.

-Robert

[alter Ratz]

Hello,

I think one point that is missing is using some Batterizer-Type switching pre-regulator for products using a linear regulator.

If you start from 1.5V and yor device drops out at 0.8V then you could pre-regulate the 1.5V to lets say 0.85V. Assuming a current consumption of 1A this would drop the battery load from 1A to 1*0.8/1.5/0.9 = 0.59A (assuming a generous efficiency of 90%), thus reducing less power loss in the linear voltage regulator of the product and (theoretically) increasing battery lifetime.

However, I did not take the time to calculate if reduced losses in the linear voltage regulator make up for the efficiency losses in the switching converter.

But however, this is not how the batterizer works (rather it does the opposite of converting the voltage up!). So the batterizer is still bullshit.

Best regards,
Bernhard

[LabSpokane]

you really flunked it, sorry! 
As others already mentioned, you did not show the power integral area correctly, i.e. from 0.8 to the discharge line only, instead of zero volt to the discharge line.
That is really annoying, and may disturb students, for whom this video is intended for, obviously.

?  So all the battery companies do it wrong as well?  If there's a STEM student who can't add or subtract a rectangular area from an integral... Oh who cares? Somebody has to drag down class averages I suppose.

I thought the presentation was perfectly clear.  Maybe those unhappy souls who don't "get" it should ask for refunds.

And I thought the 0.8V cutoff was also to prevent battery leakage. 

[EEVblog]

that could have been a nice educational video, but you really flunked it, sorry! 
As others already mentioned, you did not show the power integral area correctly, i.e. from 0.8 to the discharge line only, instead of zero volt to the discharge line.
That is really annoying, and may disturb students, for whom this video is intended for, obviously.

The numbers come out exactly the same.
Too bad if they are disturbed about it, I wanted to explain how I got the graph I showed in my Batteriser blog post.

It could also have been very easy to bust the rest out of the residue energy myth, by discharging the battery to its very limits, below 0.8V, as these energy saver gadgets claim to operate well below that voltage.

There is bugger-all energy left under 0.8V at any reasonable product current. Why do you think it's the de-factco industry standard cutout voltage and is where the graphs stops in all the datasheets?
As I said in the video, you can extract a little bit more energy out under that depending upon your applications. In most cases it's not worth bothering about.
To get characteristic plots of low current drains to see how much energy is left under 0.8V is many hundreds of hours of data logging.

It's a pity you missed that chance.

Rubbish, I can always do another video. Every one of my video doesn't have to be a tour-de-force, holy grail, be-all-end-all, the mother of all tutorials 

[EEVblog]

This video was very informative, as always, but the videos where you talk while doing screen capture of your computer screen can be a little boring. Have you ever considered setting up a camera and recording yourself while you talk? Then you can do either a picture in picture shot where your talking head is in the corner of the screen, or you can cut back and forth between you and your computer screen. Doing either of those, or a combination, would make your screen capture videos more entertaining. Sorry if this has already been brought up before, but I don't spend much time on the forums. Keep up the great work.

I don't particularly like those. I don't think my small face in corner would add any value, as you should be watching what's happening on-screen, not my head.
Also, the boom mic and pop filter is big and covers my face, and I wouldn't be looking at the camera.

[c4757p]

This video was very informative, as always, but the videos where you talk while doing screen capture of your computer screen can be a little boring. Have you ever considered setting up a camera and recording yourself while you talk? Then you can do either a picture in picture shot where your talking head is in the corner of the screen, or you can cut back and forth between you and your computer screen. Doing either of those, or a combination, would make your screen capture videos more entertaining. Sorry if this has already been brought up before, but I don't spend much time on the forums. Keep up the great work.

For those who find information boring, there is always Mailbag.

[pmj]

If i can take the data to plot the graph until 0.8v using my product as load, then I will use my product until the voltage would be 0.8v. So by this video, my product would use 100% of the capacity of the battery, what it isn't 100% true. But it is the conclusion that i would take form this method.

[dk27]

As others already mentioned, you did not show the power integral area correctly, i.e. from 0.8 to the discharge line only, instead of zero volt to the discharge line.
That is really annoying, and may disturb students, for whom this video is intended for, obviously.

The numbers come out exactly the same.

I assume you mean something other than that the apparent capacity remaining that one would get from integrating from 0.8V to the discharge line only would not differ from that if you instead integrated from 0 volts to the discharge line.  In other words, the difference between measuring the "area under the curve" with the area's base at 0.8 V instead of the area's base at 0 V.  Because, there is actually a substantial difference.

In a.png, I've sketched a hypothetical discharge curve at constant current.  (I know that no cell actually behaves as depicted, but my purpose is only to illustrate the point.)  Note that this curve drops vertically after it reaches 0.8 V, so in this case there is no energy at all after this point.

In b.png, I've changed the vertical scale to only go from 0.8 V to 1.6V, and I've asked myself the question, "The cell has been discharged to 1.2 V, what fraction of the original energy remains?".  Naively, I measure "areas under the curve" of this plot, and obtain the answer 25%.

In c.png, I keep the scale that starts from 0 V, and ask exactly the same question, now, when I correctly find the areas under the curve, find an answer which is more like 42%.  So, where we measure our areas from does make a difference.

I believe that 42% is the correct answer and that this would agree with the spreadsheet method that you spent most of the time in the video explaining.  The point though is that during the video, you did sketch over a discharge plot an "area under the curve" with a base at 0.8 V.  If we forget about the need to add the rectangles down to the base at 0 V, we are liable to be mislead, often substantially.  Even if we remember that the extra areas need to be added in, speaking for myself at least, it is very difficult to imagine the right amounts, and how this should change the interpretation.  All this is just another example of the importance of using the right scale on a graph for a given purpose.

We can always, of course, compute and get the right answer, but the importance of the graphical method (in this case sketching the area remaining under the curve) is that done correctly, it gives us an intuition for what computed result we should expect --- that's good engineering.

So, my point is that using the graphs with the given scales is likely to substantially mislead our intuition about this problem --- and it happens to do so in the direction of suggesting less unused capacity than is in fact the case.

I've been getting the feeling that in this group, saying that there is more energy left than looking at the (wrong) area suggests, makes me look like I am trying to support Batterizers (sp?) claims --- I'm not.  The numerical calculations that Dave made (with the spreadsheet), are (I think) correct, and the unbiased visual depiction of the areas under the discharge curve would support them.

[LabSpokane]

you really flunked it, sorry! 
As others already mentioned, you did not show the power integral area correctly, i.e. from 0.8 to the discharge line only, instead of zero volt to the discharge line.
That is really annoying, and may disturb students, for whom this video is intended for, obviously.

?  So all the battery companies do it wrong as well?  If there's a STEM student who can't add or subtract a rectangular area from an integral... Oh who cares? Somebody has to drag down class averages I suppose.

I thought the presentation was perfectly clear.  Maybe those unhappy souls who don't "get" it should ask for refunds.

And I thought the 0.8V cutoff was also to prevent battery leakage.

If you thought the presentation was perfectly clear can you also disclose what level of understanding you had prior?

It was a good video, and well presented but clearly some people without a solid engineering understanding of the topic still have questions.  Brushing them aside with "Oh who cares? Somebody has to drag down class averages I suppose." may suit your ego but not much else. I am glad Dave is prepared to share his knowledge for the benefit of others. In any event what is the point of an educational video to people who understand the topic?

If some "unhappy souls" still have questions, what is wrong with asking them? If it appears enough need further explanation Dave may recognize an opportunity to do a follow-up. I'm pretty sure he said he was going to get some Batterisers and test them out. It is no bad thing to have his audience well informed beforehand. And since he likes drawing graphs and analysing data it's a win all around.

I'm a EE, but I don't understand why a freshman college student with a 101 physics class behind them could not readily grasp Dave's presentation.  I was actually thinking Dave was going to show how to fit the curve to a polynomial. (For embedded, I suppose they use a lookup table of sorts.)  The graphical solution technique I thought was a great compromise.  That's how every pilot's operating handbook works and teenagers are able to work through those with no issues.  So, I'm confused why everyone's confused.  Maybe the rest of the world is so far past graphical solution techniques that they now seem strange.   

[BobC]

Sorry for posting so late to this thread, but I only now just stopped giggling.

Am I the only one who parsed the video title as: "How To Calculate `Wasted Battery' Capacity"?

My mind immediately saw a cartoon battery, laid-back and holding a joint.

So, of course, if the battery is as wasted as it looks, I doubt there's enough capacity to worry about.

Oh, come on.  "Wasted Battery".  Get it?

[EEVblog]

I assume you mean something other than that the apparent capacity remaining that one would get from integrating from 0.8V to the discharge line only would not differ from that if you instead integrated from 0 volts to the discharge line.  In other words, the difference between measuring the "area under the curve" with the area's base at 0.8 V instead of the area's base at 0 V.  Because, there is actually a substantial difference.

See attached.
As I said it makes no difference with my technique if you extend down to zero or not.
I think I now understand what you are getting at, and the confusion seems to be that you have to integrate the data under the curve. I suspect I didn't make that clear enough. The integral gives you the area under the curve.

[Smokey]

Just think of all the extra battery sales that are going on now from engineers discharging perfectly good brand new batteries just to record the discharge curves.  Time to buy some Duracell stock!

[stuner]

I assume you mean something other than that the apparent capacity remaining that one would get from integrating from 0.8V to the discharge line only would not differ from that if you instead integrated from 0 volts to the discharge line.  In other words, the difference between measuring the "area under the curve" with the area's base at 0.8 V instead of the area's base at 0 V.  Because, there is actually a substantial difference.

Nope, see attached.

Once again you're talking about entirely different things. Nobody in this thread is arguing that there is a significant ammount of energy left in the battery once it's discharged below 0.8V. We're also not saying that the calculations you did you the spreadsheets is wrong, but the graphical method you used throughout the video does not yield the same result, because you ignored a part of the energy area. dk27 and silvas posted some nice graphics to illustrate your mistake.

Edit: It seems that you realized the difference in the time it took to write this post.

I've been getting the feeling that in this group, saying that there is more energy left than looking at the (wrong) area suggests, makes me look like I am trying to support Batterizers (sp?) claims --- I'm not.  The numerical calculations that Dave made (with the spreadsheet), are (I think) correct, and the unbiased visual depiction of the areas under the discharge curve would support them.

Exactly. And just because there are some trolls on the internet trying to sell people a product that has practically no use does not mean that we shouldn't point out mistakes in Dave's videos. In fact I think that it is benefitial to correct them, becaus it prevents Batteriser from using the errors to weaken Dave's argument. In the end even with the correct calculations it turns out that their product is essentially useless.

[Wytnucls]

The 0.8V industry cut-off is an arbitrary figure, deemed necessary to avoid malfunctions in a majority of battery-operated equipment.
Since their company claims a lower 0.6V cut-off for their converter, that portion of extra energy should be measured to avoid accusations of 'not knowing enough'.
A discharge test from 0.8V to 0.6V at a constant 50mW for instance, shouldn't take more than 3 hours. That might not be sufficient energy to drive the monkey for any length of time, but should be substantial enough for a low consumption device, like a multimeter.