Mi band one ( First gen ) plastic package removed, and uncoiled: so it is a lithium polymer type battery. 3.8V 0.17 Wh 0.17 / 3.8 = 45 mAh capacity Mi Band 2 ( 2nd gen ) again a lithium polymer battery 3.7V, 0.17Wh, 45 mAh capacity So despite a newer generation, the battery remains same. The major difference is the on UI. Generation One use 4 dot size LED Generationt Two use dot matrix OLED