One problem is that I kept getting mixed messages from iRobot's tech support. Perhaps I can get something more definitive from you guys:

For something like a Roomba or Scooba, how should I handle charging? Should it be charging all the time?

MTO recommends something interesting for Segway owners: getting a Christmas light timer. They said to set the timer so that it only went on for - at most - 8-10 hours every day. That apparently helps lengthen the life of the batteries. I can do that pretty easily using my Z-Wave modules, I just wasn't sure if that was a good idea or not.