Robot Vacuum cleaner Battery compare sheet.  　 LGRoboking VR6170LVM Samsung Tango- VC-RL87V Mamirobot K7 Roomba 577 Using Hour 60min 90min 120min 90min Charging Hour 180min 120min 120min 120min Battery capacity 1900mAh 2000mAh 3500mAh 3000mAh Kind of battery LI-ION Nickel Nickel Nickel Changerble Impossible to replace individual Replacement uncomfortable Easy replacement Replacement uncomfortable Price USD 70 USD 40 USD 40 USD 60