I see a big difference in battery life when i charge it from 5% to 100%. I can get 3 days of use out of it using this method.
If i just randomly charge it 2 days is the max.
I wouldn't let it get down lower than 5% as soon as the battery meter turns red throw it on for a full charge. In fact, if i am at like 20% and need to charge before the next day i blay brickbreacker or some other game untill the meter turns red.
I am not a super heavy user but I believe the longest it has gone for me is 3 days or so.
I know there are a ton of topics about battery life floating around since basically the phone was only a week old. I am no techy or electrical/software engineer but I do believe that a more stable tweaked OS would really go a long way in stabilizing battery life in average.