I never reach even 6 hours. Normally 5 hours and half is almost 0% in Mango mode. Haaaaaaa..... Maybe next year. I will ask my local shop to replace new battery.
From 100% to 75% almost 2 hours of music, just tested. I don't know if this help. Make 2-3 full charges on the battery, I always do that with new smartphones, laptops etc.