As noted above I only got it down to 25 percent but it charged at 1% per minute. Certainly not going to get 8 hours of use out of 15%
Actually, if their claim that the battery lasts for 2 days (48 hours) is true, then coming from a 100% charge that's 0.48 hours per 1% (28.8 minutes). By that logic, in order to last 8 hours, you'd need
16.67% battery. That's not that far off if you said it was charging at 1%/min...
Now, real world test may prove or disprove this, but I've been finding that with *moderate* use and a decent signal strength, I am getting close to 48 hours per change. The problem is that in reality, we sometimes need to use our phones a lot more than "moderately" and in areas where the signal may be crap...in which case you're not going to get anywhere near that.