From what I've seen extended life batteries for phones tend to be 100-200mAh larger than stock batteries. So I think that would work out to a ~10% improvement f

From what I've seen extended life batteries for phones tend to be 100-200mAh larger than stock batteries. So I think that would work out to a ~10% improvement for most phones. It really depends on the capacity of the OEM battery. I remember seeing a 2000mAh+ battery for the EVO which would be nearly a 25% improvement over the stock battery.