What is my device's battery life?

Hi, I'm having a little trouble calculating the battery of my device. I am looking for specs online and there is so much variation I can't be sure.

I want to calculate the battery life of the Arduino Uno in sleep mode, running on two AA batteries, (and also on a 9V battery, but for the sake of this we can leave that out). In sleep mode literally running nothing!

Using this equation:

(battery capacity used before dead point) / (((circuit load) + (active load x activation time)) x (average)) = run time

Can someone help me out? I can't find these values anywhere. Maybe I'm going about this the wrong way, in which case feel free to tell me I'm wrong.


The first thing I see is that 2 x AA batteries only provide 3v, the Uno requires 5v.

The UNO draws between 40-50 mA when it’s running with no external loads connected. Although you can reduce the current used by the microcontroller to very low levels by sleeping it, other devices on the board still continue to draw power and the overall current draw will still be 30mA plus. It’s possible to build a stripped down Arduino which uses very little current - Google ‘standalone Arduino’ for information about that. There are some clones available which are designed for very low power consumption. I can’t recommend any specifically, but Google should give you plenty to choose from.