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'[EE] How much current from 2 AA batteries'
2008\01\21@051026 by

Hi guys,
I have a small question which i tried to answer without any luck using google.
Do you happen to know how much juice i should expect from 2 AA batteries
connected in series to give 3v ?
The batteries are duracell but i am also interested if someone has tested some
cheaper ones also. My design should run for one month using 2 AA batteries
and i really don't know what to expect from them
> I have a small question which i tried to answer without any luck

Try the Digi-Key catalog (http://www.digikey.com) or one of the
battery manufacturer's web sites.

> Do you happen to know how much juice i should expect from 2 AA
> batteries connected in series to give 3v ?

Define "juice".  What is the cut-off voltage for your circuit?

For non-recharable alkalines, about 2800 mAh per battery for low
load (circa 100 ohms for 2 cells in series) down to 2100 mAh for
higher load (circa 10 ohms load for 2 cells in series) is a good

> The batteries are duracell but i am also interested if someone has
> tested some cheaper ones also. My design should run for one month
> using 2 AA batteries and i really don't know what to expect from them

How much current does your design draw when operating?  What is the
duty cycle?  How many power saving features, such as sleep, have you
build into the firmware?  All contribute to battery life or a quick
battery death.

Lee Jones

> and i really don't know what to expect from them

Dumitru, you can work it out from the current your circuit uses,
the capacity of the batteries and how low the voltage can go

One month is 744 hours. If your batteries are 2000mA then the
circuit should draw less than 2000/744 = 2.7mA to run them
down to 1V each (although charts often go to 0.8V - you'd have
t check the specs of the particular batteries)

Low cost often means poorer performance. Perhaps half the
capacity of a recognised brand

On Mon, 2008-01-21 at 12:10 +0200, Dumitru Stama wrote:
> Hi guys,
> I have a small question which i tried to answer without any luck using google.
> Do you happen to know how much juice i should expect from 2 AA batteries
> connected in series to give 3v ?
> The batteries are duracell but i am also interested if someone has tested some
> cheaper ones also. My design should run for one month using 2 AA batteries
> and i really don't know what to expect from them

There are a few things to consider.

First, most major manufacturers spec capacities and curves for their
batteries at various drain levels. You'll have too find an appropriate
curve to determine the capacity you can expect. Most brand name alkaline
AA batteries are in the upper 2000, sometimes lower 3000mAh range for
typical drainage patterns. NiMH batteries are usually in the mid 2000mAh
range.

The second aspect is how low can your device go? Most curves for
alkalines give capacities based on cutoff voltages of around 0.8-1V, can
your device still work at 1.6V? If not, you'll have to derate the
capacity accordingly (you can derive this from the appropriate curve for

With those numbers in hand the math is actually very simple. Measure the
average current consumption of you device (you should already have this
since that's how you determined what curve to look at). Divide the
appropriate capacity by that number and you've got your run time (best
case).

For example, say your device needs 10mA average, and at that rate the
battery you want to use is rated at 2000mAh:

2000mAh/10mA=200hours

Note that these numbers are rough. If you use current in large pulses
you'll have to derate this number a little. Temperature will also have
an impact. And of course, cheaper batteries will likely have worse
capacity. My rule is if the manufacturer doesn't give you capacity
information, steer clear... :)

Hope this helped. TTYL
> Hi guys,
> I have a small question which i tried to answer without any luck using
> Do you happen to know how much juice i should expect from 2 AA batteries
> connected in series to give 3v ?
> The batteries are duracell but i am also interested if someone has tested
> some
> cheaper ones also. My design should run for one month using 2 AA batteries
> and i really don't know what to expect from them

One of the local TV stations in the UK did a battery test in the last
program before Christmas.

Put a set of each battery on test in one of those toy dogs that sits and
wags its tail, then intermittently jumps, and set them running to see how
long each one lasted.

Some of the brand names will be peculiar to the UK, but others are
international brands.

--- Dumitru Stama <spanacgmail.com> wrote:

> The batteries are duracell

I realize any future employment with Duracell may be
at stake, but if you can afford Duracell, you might
want to choose Energizer instead. My experience has
led me to conclude that Duracells will almost all
eventually leak.

Cheerful regards,

Bob

I had same experience, except other way around, the Energizers leaked.
Are the Duracells the ones that are dated? or some cheaper variation?
With our Airplane, the ELT (Emergency locator transmitter) required use
of the dated "D" (8 of them) duracells, changed out at 2 years. Still
have a bunch around, use them in the Maglights.

Bob Blick wrote:
{Quote hidden}

Hi Carl,

They don't leak until they are discharged. Then, watch
out! Yes, they are the dated ones(best if used by).

I only found out recently that they are under
pressure, perhaps that explains why they leak so

Cheerful regards,

Bob

--- Carl Denk <cdenkalltel.net> wrote:

{Quote hidden}

> --
On Mon, 21 Jan 2008 12:10:04 +0200
"Dumitru Stama" <spanacgmail.com> wrote:

> The batteries are duracell but i am also interested if someone has
> tested some cheaper ones also. My design should run for one month using
> 2 AA batteries and i really don't know what to expect from them

At the link below, you'll find some testing I did a while ago, for AA
cells, mostly Alkaline:

http://jcoppens.com/globo/gl4pre/bat/index.en.php   (index page)
http://jcoppens.com/globo/gl4pre/bat/lst.en.php     (details)

I was sure there was a cheapo battery (read carbon), but I cannot find it
anymore. I do remember it was about 5 times less than the alkaline ones.
Not a bargain at all!

Anyway, the tests were all with a 3.9 ohm load (quite heavy), so you will
be able to get 30 - 40% or so more over a month.

John
My usual load is 15mA but i will try to use sleep to see what will i get.
Thank you all for yout answers, they really helped. You saved me a lot of hours
of experimenting, not to mention the costs of different brands batteries :D
The capacities are not that bad after all, as Jinx said if i manage to cut down
the current to 2, 3mA by using sleep then i might be able to run my circuit for
a whole month using just 2 AA's.
Thanks again, guys

On Jan 21, 2008 10:44 PM, John Coppens <johnjcoppens.com> wrote:
{Quote hidden}

> -
Dumitru ,
You need to look at the spec sheet.
www.duracell.com/oem/Pdf/others/ATB-full.pdf
from fig 4 on page 6.  If you can put the project to sleep and only draw
micro amps, you will be able to draw more power when needed.
The internal resistance of the cell will increase as it ages.  If you
need large current draw, you might parallel a large cap to the circuit
and pull current spikes from the cap.
Best of luck
bill

Dumitru Stama wrote:
> Hi guys,
> I have a small question which i tried to answer without any luck using google.
> Do you happen to know how much juice i should expect from 2 AA batteries
> connected in series to give 3v ?
> The batteries are duracell but i am also interested if someone has tested some
> cheaper ones also. My design should run for one month using 2 AA batteries
> and i really don't know what to expect from them
>
In general, for low power systems, I've found it best to sleep as much
as possible, and when awake, run as fast as possible, so as to get
back to sleep.  The sleep-time current drain is what kills you, Run
time isn't so interesting, as long as Ton << Toff.

> My usual load is 15mA but i will try to use sleep to see what
> will i get

Sleep will make a huge difference. I've a product that uses 12mA
when it's doing something, but the rest of the time it can sleep and
use around 14nA. The batteries will self-rot before the PIC can
run them down. Shelf-life with (virtually) no drain is 10 years for
alkaline, I calculate 8,000+ years at my circuit's consumption

--- David VanHorn <microbrixgmail.com> wrote:

> In general, for low power systems, I've found it
> best to sleep as much
> as possible, and when awake, run as fast as
> possible, so as to get
> back to sleep.

The high-fuel-mileage drivers call this "pulse and
glide" :)

Cheerful regards,

Bob

On Jan 21, 2008, at 12:44 PM, John Coppens wrote:

> the tests were all with a 3.9 ohm load (quite heavy)

Most of the people who do tests do so with a heavy load.  For
light loads, you can usually look at the manufacturers data (if
you can find it.)   Here's another set: