As mentioned, screens and sensors draw power when you're "idle", unlike a dslr which is only powering the top LCD panel and a couple of digits in the viewfinder. Try shooting your DSLR with live view on all day to see just how much battery that screens and sensors can draw.
I use an Ex-Pro High Power Plus+ 1260mAh I got off Amazon for £10 as a second battery, I'd get more if I needed them, they're pretty good value.