No idea why your battery life is so bad. I shoot events and just yesterday was shooting one for about 5 or 6 hours. I have two XT2s, one with the additional battery grip and one without. I own 6 batteries total, of which 4 were in the cameras. The total number of shots yesterday was 2,350, with a mixture of mechanical and electronic shutter used. By the end of the day, I did not have to use either of my two spare batteries. In other words, 4 batteries were much more than adequate and I did check images on the rear LCD constantly all day. the batteries are all about a year old, which is when I bought the camera in the first place.
Maybe your batteries are shot, as you mentioned might be the case. Yes, there is no question that mirrorless cameras will eat up batteries faster than DSLRs, but the has got to be something wrong somewhere if you are only getting 100 shots per battery.
