i don't think, that M8 have "Best battery in world", but I think, that battery be a better of m6 M8 does progress I think, that 20 hours playing music altogether need for M8 users.
To save battery on the M6, while you are in the "Now Playing" screen, hold down the M button for 10 seconds. Your screen should shut off. Presto! More battery life.
To save battery on the M6, while you are in the "Now Playing" screen, hold down the M button for 10 seconds. Your screen should shut off. Presto! More battery life.