@digitalex, the amount of battery life you get is very dependent on many factors. In deep sleep, the core uses less than 1ma of current but the power for your sensors need to be factored in. The core can consume 250ma when wifi/cloud is connecting. @BDub did some greate work looking at battery life in deep sleep mode on another topic. I agree with @Moors7 that a power pack may be better but you will need to experiment to see what kind of results you get. 
UPDATE: The battery life work was actually by the amazing @wgbartley here: