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Voltage-capacity relation discharging an alkaline AAA battery? Answered

Let's say I have a fresh alkaline AAA battery, 1.5V, 1200mAh. Also, let's say it discharges itself with 3% per year, just lying in the shelf.
After one year, has both voltage and capacity been reduced 3%, or just the voltage? If not, how much has the capacity dropped then?

I also wonder if the battery is being discharged the same  way, when in use? E.e. is the proportion between voltage drop and capacity drop the same on the shelf while in use?



1 year ago

It's the State-of-Charge that diminishes over time. Reduction in SoC results in higher ESR (equivalent series resistance) and reduced open-circuit voltage and reduced short-circuit current (due to that rising ESR).

When you talk about the voltage of the battery, that is kind of vague. The problem is in the question. The voltage output of the battery will depend on current draw, ESR, temperature, etc. The SoC can be difficult to work out as a result, as simply measuring voltage of the battery is hideously inaccurate. Seeing if you're batteries are "bouncy" is a probably a better test than using a voltmeter. :P

Ok, thanks for a great explaination and you're right. I found some 4,5 yo AAA's and checked the voltage, which was the same as my new ones. However, they did not perform at all in my circuit.


1 year ago

Did you see Randofo's 5th step where he scrapes matches ?

Yes I saw it, and I have studied basically everything about electric matches that there is to know. But unfortunately my device can contain no flammables (or explosives). I want it to be a 100% non-hazmat device with regards to shipping. That is also the reason for not using li-io cells. I have figured that primary alkalines are the only "non-hazardous" battery with a reasonable shelf life. In addition, my device cannot be recharged. But thanks for the tip!


1 year ago


"The nominal voltage of a fresh alkaline cell as established by manufacturer standards is 1.5 V. The effective zero-load voltage of a non discharged alkaline battery, however, varies from 1.50 to 1.65 V, depending on the purity of the materials used and the contents of zinc oxide in the electrolyte. The average
voltage under load depends on level of discharge and the amount of
current being drawn, varying from 1.1 to 1.3 V.

The fully discharged
cell will still have a remaining voltage in the range of 0.8 to 1.0 V.
Multiple voltages may be achieved with series of cells "

A fully charged AAA has a 12 year shelf life...

The 1.65v -- to -- 1.30v encompasses 100% of your 1200mah battery capacity...


BTW step 5 may interest you about lighting a candle with nichrome wire..



The 1.65v -- to -- o.9v (delta o.75v) encompasses 100% of your 1200mah battery capacity and may not be linear...


In most cases, the no load voltage that indicates a state of charge should be measured at the same temperature and at least a minute after any load is disconnected...

OK, so the conclusion is that I cannot simulate one year on the shelf by using the battery until it has reached 97% of its initial voltage. Good.

I get confused by double negatives..

Me too ;)

Anyway, my experiment with the 4,5 yo AAA's was unsuccessful. Do you believe that two AAAA's in series (1,5V, 625mAh) will be more potent than one single AAA (1,5V, 1200mAh)?

Unlikely, they will have highter output resistances as the sizes get smaller, and two in series is worse than one on its own anyway.

From long experience with normal and rechargable batteries I can tell you this:
Manufacturers claims are often totally useless as they are estimated and calculated values based on a 100% perfect cell.
Shelf lifes of 10 or more years are a nice claim but without the fineprint stating the test conditions for the enviroment....
For me it does not matter if it is a rechargable battery or not, the worst enemy is no usage while sitting in a drawer somewhere.
I had top brand batteries and somehow they got lost inside a box and I found them about two years before their "best before date".
Surprisingly the voltage was still sitting at 1.68V, so I replaced the ones for my remote and took two more for a little test run.
Tiny motor with big fan blades for 3V was the work horse.
The two top brand but really old batteries (unused though) lasted for just over 8 hours before the motor was so slow that I could see the blades rotating.
Same test with new and dirt cheap batteries from the discounter: 5 hours - WTF!? ;)
Next test with brand new batteries of the same brand as the first ones and the fan kept running for a solid 12 hours until slowing down badly.
Did some more tests later on with different brands but can't remember their data.

One common thing I found helpful to check for quality alkaline batteries is their weight!
I found a clear relation (for brand new batteries) between weight and true capacity.
The heavier an alkaline battery the more power reserves you can expect.
The inital voltage might be the same for very light weights but it drops much faster compared to heavy types.
Same for what I call self recovery after a little short or overload.
Light batteries really don't tolerate this stress well and thank you with a massive capacity drop.
Quality, heavy models however cope much better here.
My conclusion also is that light alkaline batteries are quite dry compared to heavy ones, indicating a low level of electrolytes used.
And if you take them apart you often find the carbon rods on cheap types to be really thin and much softer than for quality types.

Similar but in recent years much story for Lithium based cells.
Especially the very popular types for flashlights and so on are often totally below what you might expect.
Not because of being crappy but simply because of being a crappy copy of a brand name battery!
I had several batches of "brand name" lithium cells and only after long fights with paypal I was able to get my money back for them.
As the copycats already caught up to simple checks I will sum up my findings as a little list (for fakes, cheap ones and falsly advertised ones, excluding brand name types from reputable shops):
# The protection electronics are usually left out in favour for a cheap fuse to at least prevent them from blowing up.
A quality charger will indicate the missing protection and refuse to charge.
A cheaper charger will charge them but is unable to prevent them from blowing up while charging.
The fuse usually blows when you least expect it, right after charging during first use.
# The leak protection is usually non existent in terms of electolytes leaking or bad gassing.
I had several batteries leaking the electrolyte from both ends, indicated by the wet look of the plastic covered label.
Since that stuff is really corrosive I no longer try cheap cells at all.
# Weight....
Especially for multi cell configurations like portable power banks, solar chargers with build in "high capacity lithium cells" and the likes you will often find added metal plates inside the housing and instead of 4 or 5 cells just a single one...
# A pack of "genuine Sanyo" cells just felt wrong in my hand when unpacking them.
My charger did not really like them either going from just 70% charge to full within 5 minutes.
A test in my trusted UV light showed the light goes dim already after just 20 minutes...
Since I needed evidence for paypal I dismantled one cell (totally empty out of the box and unable to charge).
The bottom third was just a hollow aluminium cylinder!

So what does that mean for your batteries?
IMHO You need to buy top quality batteries from a reputable shop if you really require a long service life at top capacity levels.
And in serious cases it pays off to contact the manufacturer and to ask for the specifics of the battery in question.
Last but not least: For the warranty you often need a proof of purchase.
The one you get at the checkout is printed on thermal paper and will fade away long before your warranty is over.
If in doubt take a digital copy of it and print it out on a laser printer.

Yes, I plan to use a premium brand AAA in my device. As you know, my project is about heating up a nichrome wire, lighting a smoke mix, with a product lifetime of 3 years. After 3 years not being used, the battery in the device must work once only. Actually, yesterday I was really lucky and found a package of 4.5 years old VARTA AAA's. The voltage was, also surprisingly, the same (1.65V) as my new package. I'll do some testing to see if they function aswell. The question is wether the old ones can deliver the same current, for about 5 secs, as the new ones. Expriements will tell.

That's probably manufacturer specific and discussed on their datasheets for the cells. a 3% reduction in voltage is often much more loss of capacity

OK I see. What I really want to find is a "self discharge curve", I suppose. Haven't been able to locate any for alkaline though.