Wow ultra battery saving mode turns the screen black doesn't it I'd hate that but two days without having that on seems insane what's your usage like heavy moderate or minimal? Are you on wifi all day? Is your signal good tell us those details then I'll judge how good it is
You do have to practice and modify some settings to get THE best battery life out of your phone. I like that I can use my phone very heavily, and can expect at least 10 hrs. I have gotten 3 days and several hours, when I used my phone moderately and lightly on EPS mode. Could have gotten more, but then what's the point, lol
I haven't been that impressed. My new phone is lasting about a day and a half with light to medium use. The MyTouch 4G that I upgraded from went 3 - 5 days on a charge with roughly the same usage. I've been monitoring the usage statistics on the HTC One and nothing is out of line.