Hi a little while ago I did a review of this Agilant 34 61a multimeter and as part of the view, I was uh, playing around with a 9volt battery like this and I made note of the fact that the reading was dropping like that and that was due to the Um 10m input impedance of the multimeter and uh, somebody in the comments sorry I forgot who it is mentioned that um, oh no, that's uh, that was me uh, holding the battery. that was my uh, you know the heat from my hand holding the battery that was causing the voltage to drop? Well no, that's not the case. Um, it is actually the input impedance of the multimeter. So I thought we'd actually take a quick look at this and just have a little play around with some basic um uh multimeter loading on various batteries like this.

Now because this multimeter is 6 and 1/2 digits, we've got for a Uh 9vt battery here. we've got 10 microv volts uh resolution here which is excellent and we can actually get greater resolution than that as I showed in the review by using the Uh data login and Uh Trend plot uh function as well and you can see it dropping. Now now this multimeter, like many um, good high-end bench multimeters and also um, handheld ones at all. It's got two different types of input impedance.

It's got 10 Meg um standard as your regular Um digital multimeter will have 10 Meg input imped and that's what we're loading down on this 9vt alkaline battery at the moment. but it's also got a high impedance mode here or high Zed it says Auto but what it's jumping to is actually High Zed You can see that on the display there, you'll notice that the voltage is now jumping back up because there's much less load on there in the case of this particular multimeter. Um, the data sheet just says it's greater than 10 gig ohms so there's a huge difference there. and uh, but um, this should be enough to let us just play around with a couple of batteries here.

and uh, note some interesting things, so let's take a look at it. Now as you may know, a brand new Uh Alkaline cell or Alkaline Manganese dioxide is the um typical chemistry uh used in these, um, most alkaline Uh batteries these days. Then the open circuit cell voltage can, um, effectively vary from anywhere from the nominal 1.5 Vols per cell or 9 volts in the case of this 9vt battery which has six 4A cells effectively inside it. If you open up one of these, you'll find um, six physical 4A size uh, alkaline cells in there, but that can vary from 1.5 Vols per cell up to about 1.65 volt per cell or for a 9vt battery up to 9.9 Vol open Terminal Uh voltage.

And this large variation is due to the Electro chemistry inside the cell and the purity of the chemicals in there and the materials and oxide layers and layers that form on the plates. And you know all sorts of um, stuff like that. So it does vary a fair bit and that will come into play when we try and measure the internal resistance of uh, a battery like this just using the load on our multimeter here. Now if you have a look at the data sheet for a typical Duracell Alkaline Maganese Diox side battery I.E Your typical alkaline battery, they're pretty much all the same.

uh, the brands. Really, there is not going to be a huge amount of difference. All the typical values are all going to be the same. Now, the Josol one happens to tell you the internal impedance of this thing.

there it is 1,700 milliohms or 1.7 ohms. Now that value of the internal impedance is actually uh, fairly consistent across the life of the battery. It really doesn't change much at all. and that's the basic electrical uh, contact resistance inside the cell itself.

Now this is really a key point because it's specified at 1 kilohertz here. and the reason it's specified at 1 kilohertz is because uh, it doesn't include What's called the ionic resistance or the electrochemistry effects as you uh as I often uh call it inside the cell. So that's why if you really want to measure the internal impedance of the battery the internal es some people call the ESR then you have to do it very quickly at a rate around about 1 khz or there abouts. It can be a bit slower than that, but it can't be in the order of seconds.

so it's not like you can hook up your battery and then a couple of seconds later take a measurement and then you know, do your Ohms law calculations and see if you can calculate that 1.7 Ohms Because if you won't get it because over the longer term period of you know, hundreds of milliseconds to seconds to minutes to hours, it's the ionic resistance or the electrochemistry effects inside the battery that dominate so that internal impedance is only valid at those very short time periods there. Now that warrants a separate Uh video in its own right, How to actually measure and confirm that internal impedance? We won't be able to do that here today because as I said, you got to do it very quickly. You usually have to set a St It's usually done with a uh, a pulse um, load where you set a stabilizing pulse and then you drop the load uh, right down and then you measure it straight away and then you take it back up really quickly at near that 1 khz rate. But if we have a look at the Uh typical discharge characteristics of this cell, it's not that 1.7 Ohms that value of the ESR that's increasing under low that's causing the discharge of this cell.

It's mostly the ionic resistance at play here over these long time periods and you'll notice that it actually uh starts very high and then ramps down very quickly. It's not very noticeable on this one, but if we jump over to an Energizer data sheet once again for the same 9vol battery, you can actually see down here. where for it's this one's you know, not a particularly High uh load. and it is uh, pulsed and in in this case, it's 10K 620 ohm 1 second uh pulse per hour.

So you know a fairly light, light, fairly light pulse load. You can really see the rapid drop in the value here. and that's the electrochemistry or ionic resistance coming into play. And not only does it uh, come into play over days like we've got here, you also um, and at fairly High loads.

This also has a similar drastic drop effect as we'll see in a minute over very short time periods, in in terms of uh, seconds, and under some un and under some unusual scenarios which will also show in a second so we'll get a very S. We should be able to get a very similar drastic drop like this, but over very short time period. so it'll be a similar sort of Uh graph to this one. So just remember that 1.7 ohm value and how it will basically be unmeasurable in the stuff we're going to do today.

It won't have an effect at all, yet You will still see the voltage drop on the battery very similar to this sort of thing because it's not the internal impedance at play. So that is why if we set our multimeter to Uh 10 Meg input impedance like that, we're going to get a fairly dramatic drop like that in In, in the Uh in initial drop anyway of the voltage of the cell. Now it will actually start out and drop exactly like we saw on the Energizer graph. There start out very high drop dramatically and then sort of taper out and uh, sort of stay steady.

So if we leave that there long enough, we will actually see that that stay. That value will eventually stabilize. Now with a 9volt battery and a 10 Megga Oh impedance on our multimeter Here, we're only talking 900 nanoamps and of course, 900 nanoamps times 1.7 ohms internal resistance. We're only talking about 1.5 microvolts, so really, you can't even see 1.5 microvolts on here.

It's the next digit over effectively, so you know, really? Um, we're just being swamped by the electrochemical effects here, so we can't actually see our internal resistance of our battery. Uh, just based on the very light load from this multimeter. But let's have a little play around with this because we can. let's go into into a high impedance, uh mode or 10 gigs and let's go into the display and go into the trend chart here.

So what I'm going to do is I'm in the Uh 10 gig ohm High Zed uh state. So we're only talking with 10 gig 900 uh pamps across a 9volt battery so there effectively no load at all. and if you multiply that by the internal resistance, you know we're down at 1.5 nanov volts. Absolutely tiny.

But anyway, let's hook that up and then we're in our Trend chart mode. So let's actually reset our readings on our Trend chart here and see what we get. So there we go. I've a auto scaled that and as you can see, it's sort of.

You know it is pretty flat because it's had time to stabilize from that dramatic 10 megga ohm load by the way. So what we're going to do now is we're actually going to turn on our 10 Meg uh load. And of course, if you're just talking about the internal resistance of that uh battery. As I said, here's our voltage here.

now. We would expect it if it's just based on the internal resistance or the nominal internal resistance. So 1.7 ohms. once we put that 10 Meg on there.

If it's just due to the internal resistance of the battery, then we'd expect the value here, which can see the numeric result to only drop by 1.5 microvolt. so we shouldn't expect to see any drop on out at all. But let's do it. Let's switch it on 10 Meg and Bam Look at that, it's dropped right off the scale.

So much so that we have to go back in here and auto scale that again and you can see it drop down fairly dramatically. You know it's fairly well stabilized there. Now you know there's still a bit more to go, but let's turn it back and we'll watch it jump back up. There it goes.

Look at that and it should curve back up to our original terminal voltage up there. So we've got some funky, very low load, incredibly light load electrochemistry effects happening within the battery there. Now the original commenter said, uh, that that drop, of course, had to do with the uh, temperature of my hand in the battery and that actually has, uh, nothing to do with it at all. It's demonstrated that it was actually the load doing that.

But let's clear this. okay. I'm back to Um 10 Meg input impedance here now. Oh, sorry.

I'll uh, get back to displaying recent data. There we go. That's better. There we go and watch what happens though.

This is quite fascinating. Okay, watch what happens if I squeeze this battery. Woohoo. Look at that.

Let's autoscale that again. Squeeze again. Look at that. It's jumping all over the shop, just squeezing it.

Um, it's electrochemistry effects once again causing that to happen. And if we switch back. Oh, in. in this case, it's not physical.

There's some physical process inside that battery. Let's go back. autoscale it again. And here's where we have to let it settle and stuff like that.

So this is with a 10eg load. let's give that a little squeeze. Look at that. There we go and it's still doing it and it's no, it's not the leads or anything like that.

I mean you know I can move this around here and you know it's it's not the contacts I can sort of. You know I mean if I really play around with it, we might be able to get some um, something to do with the contacts. but that is physically me squeezing that battery. Or if I put it down like that, here we go.

Let's Auto scale again. There we go. Look at that. Fascinating and we can put it side on like that.

Bingo it does exactly the same thing and that that is effectively changes in the ionic resistance of that battery due to physical pressure. That was an absolute Ripper look at that. We got a really got a negative uh going P pulse there so that is absolutely fascinating. It takes time to recover because it's the chemical ionic uh processes within the battery that are actually doing that and I'm sure he could do a a whole PhD thesis on examining exactly what you know is going on.

um in various uh cells of different uh chemistry, in terms of pressure, temperature and discharge, current, and initial uh loading, uh discharge and all sorts of you know, all sorts of stuff. But I find that absolutely fascinating. And I've been playing around with this battery quite a bit. So what I'm going to do is actually just, uh, repeat that with a brand new uh Duracell So let's whip this one out of the Uh packet and give it a go.

Here we go. Let's put it on. Never been loaded, All right. Clear readings and auto scale.

There we go. it's dropping down. Oh, we've got the yeah, we got the 10, got the 10 Meg load on. Oops, let's let's put the auto on.

There we go. So we got our 10 gig impedance and that recovered fairly quickly there. But you can see that even with a 10 G gig load or greater than 10 gig, the data sheet doesn't actually tell you the um, exact value of it, but let's assume it's just 10 gig. that's still only 900 Pico amps load on that thing and we can still see the discharge curve of that.

Absolutely incredible. There we go. Look at that. that'll take quite some time to stabilize.

and let's see if the Durac cell has that same effect where we can apply high pressure to it and well, yeah. I saw a little little blip in there. We? yep, there we go. look at that.

but it's a different. looks. like it's a different effect to our V battery. Check that out.

I've actually effectively changed the slope of the discharge of that cell just by oh, that battery. Sorry, it's not a cell. it contains six cells just by squeezing that. Absolutely fascinating.

You can see it's starting to recover there in terms of uh, slope. but let's uh, actually switch on our 10 m load now and see what we get there. We go. We're dropping about 10 microv volts there per second or thereabouts.

but uh, that one didn't show a dramatic as dramatic effect. Um, with the 10m load as the V battery did with its or I I don't know the history of this V battery by the way, it just came out of my drawer. may have used it once or twice in something and can we see the same effect with a Able A? Well, I've got a V long life ablea battery here. Um, brand new Straight Out of the packet unused and let's take a look.

I've got it in the high impedance modee at the moment and uh, there you go. It's fairly flat, it's fairly stabilized, and we can go back. and we can Auto scale that, of course. Uh, sometimes it doesn't Auto scale to the center.

But anyway, we should be able to see if there's any pressure effects in this one too. So let's it's sort of harder to put a bit pressure on a Able A, but you can see that. Yeah, look at that. It's let's Auto scale.

Uh, Auto scale that. Check it out. We did get a drop there. will it recover? I don't know.

we'd need some time to actually find that out and I've left it for just over 20 minutes here and you can see that it didn't recover at all. There's that little period there where we where we actually press the thing, step down and looks like I permanently hurt the poor little bugger and uh, it never recovered at all. permanently dropped his voltage and you can see that there is a ramp down very slow little slope there drop in voltage over that time. now whether or not that's due to the trauma I guess of actually pressing that cell whether or not it's the uh, very gentle once again still uh uh High impedance load on this thing or not I don't exactly know.

but anyway, it's interesting and once again, if you're wondering no, it doesn't really have anything to do with the context I've just got my alligator uh Clips hooked on here and you know I can play around with this thing and and give it a bit bit of a uh, bit of a go there and really, hey, look at that. maybe a little slight something happening there, but it's not the contacts going dodgey or anything like that, especially at these incredibly low loads. and you can actually see the recovery of the ablea V cell there when it went down to 10 megga ohm load and then I uh set it back to high impedance mode and it ramped up up over the span of about 30 minutes. Right back to the original value up there.

And you can see with the Ablea battery here how we dropped down to I was playing around with it down to 10 uh Megga Ohms load there. Then I switched it back to high impedance and look at the total time 30 basically 30 minutes there to slowly ramp back up right up back to the original value there. That shows you how slow changing the this you know ionic electrochem is inside these cells. Really quite a slow process.

And look at the values we're talking about here. We're barely talking about uh, 100 microvolts there. total change fourth decimal place stuff I mean really small values, but 6 and 1 half digit meter like this with the ACT actually it's more than 6 and half digits when you're in this uh Trend chart mode can really show you these differences. One of the benefits of one of these really, uh, high resolution digital multimeters.

And here's a brand new Duracell fresh out of the pack. Uh, long expiry date and it haven't loaded it with 10 Megga Ohms. it's on the 10 gig ohm thing. so this thing has never been loaded out of the box and you can see it dropping down you know, fairly consistently like that until it'll get to a point where it's going to stabilize fairly well.

And that is, even for that incredibly light 10 gigm load. Absolutely incred. incredible. And check that out.

after 6 minutes, there's our initial drop we saw before and I thought it was flattening out, but now it's sort of recovering a bit and there you have it. it's practically recovered to exactly where it was straight. Factory Fresh there. So that initial dip was due to the 10 gig ohm load on there slowly recovered.

Well, let's see what happens if we, uh, give this thing a little pressure test. No, hardly anything at all on that fresh. Durell Oh no, there we no. There we go.

Got a little something there, but not much at all. and Just for kicks, we'll go back to the 9volt battery, but this time Energizer Fresh out of the pack. Let's give it a go. Here we go: 10 gig load so never been loaded fresh out of the pack.

Clear that and we will Auto scale and bingo There we go. We get that initial drop again every time and that's over 14 minutes there and you can see that we haven't had any recovery at all. but we have had a change in slope. I Mean you can see the big large slope there and it flattens out a bit and then we've got sort of another slope down in here so it's gradually taping off, but that's after after almost 15 minutes.

Now can we actually get a pressure change in that? Well, let's give it a go. No. I'm going to have to switch out of the recent mode. Yeah, there we go, we've we've got it to change.

Auto scale. Yeah, there we go. We changed the slope of once again going downwards just like the Duracell one and opposite to what we saw in the Vada battery. And there we go.

It's starting to level back out. so like let's give that a squeeze again. Yep, there we go. Pressure effects once again and let's see what happens if we switch to 10 Meg mode.

There we go: 10 Meg and once again, we, yeah, we don't get a huge drop at all. So that brand new Energizer out of the packet effectively shows very little difference at all there. Uh, between between the 10 mega ohm impedance and the 10 gigm impedance that purely because it's totally Fresh So that V battery we were playing with at the start? Uh, obviously had a little bit of uh use in it and wasn't you know directly? Factory fresh like this Energizer one or the jisol. And just for more kicks, we have a Kohl's brand battery I have uh, no idea who actually manufactures this one, but we'll give this a go check out that one.

We got a sudden drastic drop there and that wasn't me touching this thing at all. that oh look look at that look at that isn't that unusual. What's going on there? That is really really weird. Wow, look at that.

let's uh, turn on. Oh look, see another drop. I swear I'm not touching that I am not touching that at all I won't even breathe on it. Very interesting.

Let's see what happens if we switch our 10 megga load on there. Oh wow, look at this. this fresh Kohl's battery straight out of the packet. we've got ourselves a big drop like we got on the Vada one.

So maybe that Vada one wasn't used. Maybe it's just the physical construction is different and the chemistry is uh well yeah well, the chemistry is technically the same, but uh, there we go. Yeah, we got the same thing we see in the Vada battery. So there you go.

It's not a Vada battery this one I know cuz this one's made according to the packet in South Korea and uh, yep and the Vada one is made in Germany So there you go. But basically exactly the same thing that we saw in the Vada battery. so that V Vada battery um I was fairly new that fairly sure that hadn't really been used. Maybe for you know, 5 minutes in something.

very light or something at best, but it look looks like this is Cole's one has confirmed that effectively. Durac cell on the Energizer ones are almost identical in terms of their response. Um, but this one is very similar to The V Almost identical so let's see if that should recover. Now if we, uh, turn that load back.

Yep, yeah, it works exactly the same as the Vada look at that. So I reckon that Vada one was actually brand new and this one has confirmed it. so that was well worth doing that. Kohl's one that was very, very interesting.

Now let's see what happens if we do the squeeze test. We're pro. Actually, I won't touch that. We're probably better off uh, clearing that, actually starting a fresh there and oh, I'll just turn it off there.

So Auto scale and ah, let's not wait. come on. I can't wait. Let's give that a little press.

Yep goes up just just like the Vada one. confirmed two different types. We've discovered two different types of alkaline construction 9vt batteries. Wow, that is fascinating.

There's yeah. squeeze again, it's done exactly the same thing. Woohoo! This is great I Love playing around with stuff like this. So there you go.

I hope you found that interesting and you uh, learned some something there and uh, of course this isn't you know, a scientific uh test. This was just a little quick. uh, throw together to show you that well to show the original YouTube commenter that had nothing to do with the temperature of my hand. it was actually the load.

Even the incredibly light load of the multimeter combined with the electrochemistry and the ionic resistance in the battery that was causing those drops. But we also played around with the fact that these things are pressure sensitive. If you like that video, uh, please give it a big thumbs up on YouTube CU That always helps a lot, and if you want to discuss it, jump on over to the Eev blog Forum that's the best place to do it. although you can always leave comments in YouTube as well.

And uh, if there's enough interest, maybe I might, uh, follow this up with some more testing. But if you've got a high resolution multimeter like this, have a play around with this cuz this sort of stuff is absolutely fascinating. It would be interesting testing to see what results we can get if we, uh, do some more scientific, uh, you know, more methodical testing on these things. But there you go.

Catch you next time.