my experience somfar with the W812a v.1,2,0
7 hours = 4% battery usage without data connection (during night)… so far 12 hours and still have 54 % battery left…i have only 3G and in roaming all the time ( cant find a way to take off roaming)
…country :sweden
Carrier: 3 sweden
really noce rom and battery saver nr.1