I also got these off Amazon, and my first full day I went from 7am until about Midnight and I was 20%. However the second full day I went from 8am until 1am and I was still at 40%. I have tried the 1300, 1500, 2150, and 3500 mah batteries aside from this, and I am going to stick with this one. My 3500 will be going up on ebay sometime this week.