Thanks for your explanation.
My guess is that the pro mini should draw more towards 1 mA instead of 100, by using the powerdown command and only waking up once every 15 minutes to do a measurement (and act on it if necessary) and removing the power LED. Which would mean 0,08 watt hrs/day if i calculate that correctly (using 3.3v of the pro mini, not the 5v version). that + 0.17 watt hrs/day for the stepper = 0.25 watt hrs/day...
In that case 2.5 watt hrs/day would be more than sufficient, even with chicken sh*t taken into consideration... would those numbers be realistic?