Hi Rafael,

Looking at the XBEE webpage, they spec the supply voltage at 2.8V to 
3.4V so you cannot discharge a 3 volt battery very far before you are 
too low to operate.

Battery manufacturers rate amp-hours with no regard to terminal voltage. 
  Especially for consumer primary batteries.  Their curves usually show 
running the battery down to half of it's original voltage and measuring 
how many amp-hours that produces.

I did not see any information at the XBEE site about what they mean 
concerning battery life.  But it looks like they expect you to figure 
out how to extract all the amp-hours regardless of terminal voltage.

 From your information you posted, it looks like a switcher could help 
you out.  A boost configuration should get you where you want to be.

Good luck!

Rafael Vidal Aroca wrote:
>     Hi people,
> 
>     i'm playing with these great ZigBee modules from Maxstream (XBEE). 
> They are really interesting and powerful..
> 
>     My problem is related to battery life.
> 
>     According to the manufacturer battery life calculator available at:
> 
>     http://www.maxstream.net/support/battery-life-calculator.xls
> 
>     i could have a life of more than 3 years depending on the conditions 
> i use my modules. Well, my conditions are quite good:
> 
>     - The module is in sleep all the time, waking up each 4 minutes, 
> sampling ADC ports, transmitting data, and going back to sleep
> 
>     Theorically i should get at least a year, but when i tested it, my 
> batteries did not last for 2 months! I'm using 2 alcaline AA batteries 
> which gives 3V.
> 
>     Well, seems like the batteries still have energy, but their tension 
> has gone to less than 2,7v, which will not power XBEE.
> 
>     The problem, is that there are no commercial batteries available 
> with 2000mAh and 3 ou 3,3V with low voltage drops in the long time.
> 
>     Some engineers suggested me 9v batteries with a voltage regulator.
> 
>     Is it a good idea? Won't i loose too much in the voltage conversion 
> (9-3=6v). At 50mA i'll spend 300mW just to drop the voltage???
> 
>     Well, i really don't know how to manage the batteries to give me 2 
> years of life to my little remote sensor.
> 
>     Does anyone have any idea or clue?
> 
>     thanks a lot
> 
> Rafael

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