I've just completed a simple temperature measurement project. As there's no power source like a wall plug, I'm using a 9V battery.
My first try was a Duracell MN1604, my second one was a rechargable Varta HR 6F22 (200mAh). Unfortunately I could not even power the project for 12 hours. After 12 hours the temperature sensor (SHT15) does not get enough power to work, leds don't light and so on. Only the power control led on the arduino board is glowing very dim. When I connect the project to a new battery or USB, everything works well.
So I suspect that the battery life of my Arduino project is only a few hours.
Is this a normal condition or could it be that my circuit has some sort of leak?
How much current does an Arduino draw if I run just the board itself? If, for example, it would draw 20 mA then the reason why it stops working after 10-12 hours would be clear as the Varta I tested has a capacity of 200 mAH. So the solution would be a larger battery pack!?