The ML-RMB400 Replacement Battery by Mighty Max is Designed for for iRobot Roomba APS 400 Series, Its an Ni-Cd Rechargeable battery that keeps Roomba running at peak performance, cleaning up your room in a single charge. ML-RMB400 can be charged or discharged as needed without loss of capacity. The ML-RMB400 battery is fully compatible with all Roomba FloorVac models: iRobot Roomba 400 Series, Discovery Series, Create Models and Dirt Dog Models.