# AA battery energy estimate

Hi all,

I'm using NS2 to simulate wireless sensor networks. I want an estimate of the initial sensor battery energy. I know that each sensor node uses 2 AA batteries. I have no assumptions about the current. I search for a while on the internet but couldn't find a direct estimate.

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I have seen that link before .. but I feel that the numbers are very large! Is it possible for such a small battery to store such big amount of joules?
Is there any other place that I can validate these numbers from?

Why do the numbers feel large? Looks like the biggest energy storage in a AA battery is like 3 Calories. A joule is a very small unit.

russ_watters
Mentor
Most people are surprised when they first find out how much energy things use. We occasionally get people in here asking stuff like how long they can power their house by lowering a ton of concrete 10 meters to drive a generator and they are shocked at the answer.

sophiecentaur
Gold Member
I agree.
There is a huge difference in the amount of energy needed to move something around compared with heating it up. So much so that it goes against our intuition.

But compare how much food mammals need, compared with fish. That says it all.

berkeman
Mentor
Hi all,

I'm using NS2 to simulate wireless sensor networks. I want an estimate of the initial sensor battery energy. I know that each sensor node uses 2 AA batteries. I have no assumptions about the current. I search for a while on the internet but couldn't find a direct estimate.

To estimate the battery life for a wireless sensor node (something I have done in detail), you start with the datasheet for the battery:

http://data.energizer.com/PDFs/E91.pdf

and use the discharge curves to see how much time you can get current out of the batteries at a reasonable voltage. For the current, you use the active and standby currents, and the on/standby duty cycle that you are designing to.

There are tradeoffs in using a DC-DC (boost/buck or sepic) converter to try to extract all of the energy out of the batteries. You would need a very efficient DC-DC to justify using one. For one design that I worked on, it turned out to be optimum to use 3xAA batteries, in order to get the best battery life in a fairly small package. Using 3 in series let us meet the RF circuit and the microcrontroller voltage specs, even at the end (85%) of the life of the alkaline batteries.

I have seen that link before .. but I feel that the numbers are very large! Is it possible for such a small battery to store such big amount of joules?
In some respects the numbers may in a sense seem large....BUT everytime time I check an electronic device, such as a TV remote control for instance, I find that it stops working at perhaps 1.35 volts vs maybe 1.52 volts when brand new....thats a huge difference in capacity relative to a discharge voltage of say 0.8 that I just saw on the energizer site....that might be ok for a flashlight with a rather dim light, but I have not come across electyronic devices that will tolerate that.