tens of years battery life ?

[kellogs]

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]

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

 

[kellogs]

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

 

[kpatz]

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]

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]

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]

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]

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.