To force a second run from your 450, after the first run is finished, go ahead and clean the tank then refill the tank as usual then place it on the floor. press down the ( ! ) and Clean button at the same time then press the Room size button once and release all buttons. The Scooba will prompt for room size. Press the room size button for the size room you want to clean then hit the Clean button and away it goes. You just got a second run on the same battery without a intermediate charging cycle. Enjoy you cleaner floor.