Why are NiMH 1.2v instead of 1.5v

Ok, so it's another dumb question, but I haven't seen the answer yet. I'm sure it's probably here somewhere, but I can't find it.

Why are NiMH batteries 1.2v instead of 1.5v? If they are supposed to be a replacement for Alkaline, why not 1.5v? I can't believe it's a technology issue. Maybe a marketing issue, to keep Alkaline alive, so why 1.2v?

Thanks, and it also goes for all the Li-ion, LiFe and others, why not have them standardized? I'm not educated enough to go figure it out myself, but it seems strange that we have to have 3.0v, 3.2v, 3.7v, etc.....

It sure would be a lot easier if they were standardized, wouldn't it?

jaygrant said:

Ok, so it's another dumb question, but I haven't seen the answer yet. I'm sure it's probably here somewhere, but I can't find it.

Why are NiMH batteries 1.2v instead of 1.5v? If they are supposed to be a replacement for Alkaline, why not 1.5v? I can't believe it's a technology issue. Maybe a marketing issue, to keep Alkaline alive, so why 1.2v?

Thanks, and it also goes for all the Li-ion, LiFe and others, why not have them standardized? I'm not educated enough to go figure it out myself, but it seems strange that we have to have 3.0v, 3.2v, 3.7v, etc.....

It sure would be a lot easier if they were standardized, wouldn't it?

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Yes, it is indeed a dumb question. Why is the sky blue and not red? Why are plants green and not blue? Why aren't humans all the same size? It would be a lot easier for clothing manufacturers if all humans were standardized, wouldn't it?

It's just a result of the chemistry.

Mr Happy said:

Yes, it is indeed a dumb question. Why is the sky blue and not red? Why are plants green and not blue? Why aren't humans all the same size? It would be a lot easier for clothing manufacturers if all humans were standardized, wouldn't it?

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Thank you so much, it's why I hardly ever post here.

sfmartin said:

It's just a result of the chemistry.

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Thanks.

So the chemistry couldn't have been manipulated for a .3v difference in the result. Hmmmmm.:thinking:

I'm sorry about the tone of my response. It was meant in good humor.

Sometimes it does astonish me though that people think the laws of physics can be bent according to human will. The reality is that the laws of the universe are what they are. Science consists of discovering them and documenting them, and engineering consists of using them to best advantage.

The voltage of a battery is completely determined by the chemicals within it. You cannot change the voltage without changing the chemicals, and if you change the chemicals the battery may no longer work as desired.

The 1.5V nominal voltage of alkaline cells drops (sags) almost immediately under load.

As donn says, the voltage of an alkaline cell really isn't 1.5 V, as you can see in this very informative document: http://data.energizer.com/PDFs/alkaline_appman.pdf

jaygrant said:

Thanks.

So the chemistry couldn't have been manipulated for a .3v difference in the result. Hmmmmm.:thinking:

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You also have to realize how those numbers are calculated. Alkaline 1.5v is peak voltage. Under load, they almost immediately sag below 1.2-1.3v.

NiMH start out around 1.38v, and maintain >1.2v under heavy load. Compared to alkaline, they will maintain a higher voltage under load over the majority of a discharge.


And yes, it's simply because of the chemistry. Each electrochemical battery type has it's own unique nominal voltage produced. The chemical cocktail used is what decided the voltage. It's much easier to make good cells and adapt to their voltage than to standardize on a single voltage and suffer crappy cells which are negatively altered to produce ONLY that voltage.

jaygrant said:

Thanks.

So the chemistry couldn't have been manipulated for a .3v difference in the result. Hmmmmm.:thinking:

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Nope. It has to do with the reduction potentials of the materials used in the various types of cells. To change the voltage, you'd have to change the materials, and if you change the materials then you no longer have (for instance) an NiMH cell.

The theoretical voltage is a function of the composition of the active materials in the anode and cathode for the cell.

For a NiMH cell, you have:

Anode, MH
Cathode, NiOOH (nickel oxyhydride)

During discharge, the cathode is reduced to nickel hydroxide and the anode oxided to metal alloy M:

NiOOH + H2O + e ->Ni(OH)2 + OH-, E = 0.52V
MH + OH- -> M + H2O + e, E = 0.83V

The overall reaction is

MH + NiOOH -> M + Ni(OH)2, E = 1.35V

The anode potential above assumes a particular wt% of H2. The nominal voltage is typically given as 1.2V, but it depends on temperature and discharge current. You get a voltage drop under load because of non-zero internal impedence of the cell itself, producing a V=IR voltage drop.

jaygrant said:

Ok, so it's another dumb question, but I haven't seen the answer yet. I'm sure it's probably here somewhere, but I can't find it.

Why are NiMH batteries 1.2v instead of 1.5v? If they are supposed to be a replacement for Alkaline, why not 1.5v? I can't believe it's a technology issue. Maybe a marketing issue, to keep Alkaline alive, so why 1.2v?

Thanks, and it also goes for all the Li-ion, LiFe and others, why not have them standardized? I'm not educated enough to go figure it out myself, but it seems strange that we have to have 3.0v, 3.2v, 3.7v, etc.....

It sure would be a lot easier if they were standardized, wouldn't it?

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Same reason full-size SUVs don't get 100mpg. It's a conspiracy by the man to keep the common folk down.

Itchrelief said:

It's a conspiracy by the man to keep the common folk down.

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Just because I'm paranoid doesn't mean there isn't a conspiracy. Don't let the man try to put you down.

Great questions! I've wondered if the limitation was chemical or technology.

Marduke said:

You also have to realize how those numbers are calculated. Alkaline 1.5v is peak voltage. Under load, they almost immediately sag below 1.2-1.3v.

NiMH start out around 1.38v, and maintain >1.2v under heavy load. Compared to alkaline, they will maintain a higher voltage under load over the majority of a discharge.


And yes, it's simply because of the chemistry. Each electrochemical battery type has it's own unique nominal voltage produced. The chemical cocktail used is what decided the voltage. It's much easier to make good cells and adapt to their voltage than to standardize on a single voltage and suffer crappy cells which are negatively altered to produce ONLY that voltage.

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That's an awesome answer.

This kind of information is requested enough that I keep a couple bookmarks:
Battery Myths vs Battery Facts

IIRC Rayovac had some 1.5v rechargables. Don't know if they still make them, but I had some AAA's. I think they called them rechargable Aliklines or something?

Also Nimh's when full charged can reach 1.5v. If they were rated at 1.5v, they would probably be like 1.8v off the charger and perhaps for some sensitive devices, this wouldn't be good.

jasonck08 said:

IIRC Rayovac had some 1.5v rechargables. Don't know if they still make them, but I had some AAA's. I think they called them rechargable Aliklines or something?

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The performance was terrible, much lower than a regular alkaline. Each time they were used they lost capacity and they were extremely prone to leaking as well. What's not to love?

The 1.2v VS 1.5v is what keeps my LED grill lights (to be used on a cooking unit, not an automobile) from working on eneloops :thinking:



Ok, with three batteries it is 3.6v VS 4.5v so that is a little more of a difference

jaygrant said:

Why are NiMH batteries 1.2v instead of 1.5v? If they are supposed to be a replacement for Alkaline, why not 1.5v? I can't believe it's a technology issue. Maybe a marketing issue, to keep Alkaline alive, so why 1.2v?

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I think this is a very good question. Why are they labelled differently? Neither Alkaline nor NiMH are 1.5 or 1.2 V, respectively. In most application the nominal voltage of NiMH are higher then in alkalines. NiMH initial voltage is somewhere >1.4 V. Where is the logic here? It seems that the labelling convention for primaries and rechargables are different.

The only reason I can spot for making this 1.5/1.2 V distinction is to make clear that you are dealing with different kind of batteries? Or may be NiMH users are smarter and can handle the truth better?:naughty:

Has anybody some insight on this? I don't think the "It's chemistry man!" quite cut it with AA batteries.