Hi Alexander,
The board itself does not take much energy. I use two AAA battery's and it works fine for about a day. To be sure you could use AA battery's instead if you have a lot of power consumption (when using a LCD screen for example it goes much farther then when you only measure sensors). What are you going to combine with the Arduino? I combine my switches with 10K resistors and I have 10K potmeters.
Hans.