ML621 lithium button cell is rechargeable, with a 3.0V & 2.5V working voltage, 6mAh, ideal for using on watch, electric toys..  

Model	ML621
Nominal Voltage	3.0V
Standard Charge/Discharge Current	0.05mA
Cycle Life	60~100 times
Temperature Range(centigrades)	-20~60
Weight	0.35g
Application	Watch, medical apparatus, thief alarmsetc

lithium button cell ML621