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tens of years battery life ?

kellogs

Jan 7, 2014
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The device is a I2C transmitter + AVR 8bit MCU. It transmits for about 10 ms @ 10 mA every 20 minutes or so. The rest of the time I set up the MCU in sleep mode drawing some 4 uA.
My calculations for 2xAA alkalines, useful voltage range 1.8 - 3.2 V (considered 2200 mAh as useful capacity), at room temperature yielded some 49 years of service.

Is that way off ?
 

Alec_t

Jul 7, 2015
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According to Battery University, alkaline cells have a self-discharge rate of 2-3% per year. Have you taken that into account?
 

kellogs

Jan 7, 2014
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No I have not. I figure still some 20 years will be left. It still seem like a huge service life.
 

kpatz

Feb 24, 2014
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Most alkalines won't last 20 years left in the package. They usually self discharge and/or leak long before then.

If you need something to run that long without external power, could you use rechargeable cells and a solar panel? Even rechargeables don't last forever, but with that light a load and gentle charge/discharge cycles it should be able to run for a really long time.

Lithium primary cells (which are available in AA form) will last a lot longer than alkalines.
 

Nanren888

Nov 8, 2015
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Not something that I do every day, but, ...

(2.2Ah * 2) capacity of two batteries (Room temperature)
(0.01*0.01*3) drain per hour
(2.2 * 2)/(0.01*0.01*3) = hours of life = 14,667 hours
14,667/(24*365) = 1.67 years
.
Did I go wrong?
 

kellogs

Jan 7, 2014
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Not something that I do every day, but, ...

(2.2Ah * 2) capacity of two batteries (Room temperature)
(0.01*0.01*3) drain per hour
(2.2 * 2)/(0.01*0.01*3) = hours of life = 14,667 hours
14,667/(24*365) = 1.67 years
.
Did I go wrong?

I think so. Firstly there is 2.2Ah only as the cells are connected in series. Secondly if you divide Ah by A/h (measure units of drain per hour) then the 14 667 is not hours but hours squared.
My guess is that the second line it would rather be 0.01 Amper * (0.01 second / 3600 second).

Did i go wrong ?
 

dave9

Mar 5, 2017
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I don't assume alkalines will last more than 5 years in use without leaking and even then, I don't use alkalines for any use where over 2 years is expected. Capacity calculations are meaningless compared to the device damage and hassle cleaning that up.
 

Audioguru

Sep 24, 2016
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Energizer guarantees a 10 years shelf life for their alkaline batteries. I have used many and never had one leak. I have seen many leaking Duracell and Super-Heavy-Duty batteries.
 
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