Battery life is somewhat random; it's why batteries as a whole are measured with MTTF. You may be lucky enough to have an outlying battery life, or you may hav

Battery life is somewhat random; it's why batteries as a whole are measured with MTTF. You may be lucky enough to have an outlying battery life, or you may have used the phone in such a way that the battery lived longer, or the battery itself may have had a higher MTTF due to it being a larger capacity.