1pcs Battery For Mint 4200 and iRobot Braava 320 Series 7.2V 2600mAh NI-MH HOT! 618952363182 | eBay
Amazon.com: HQRP 2200mAh Battery Works with iRobot Mint 4200, Mint 4205, Braava 320, Braava 321, 4408927 Automatic GPHC152M07 Ultra High Capacity [Robotic Vacuum Cleaner] : Home & Kitchen