I believe you can pull quite a few boards off the Haas (with the power off) without loosing anything. At least I have
I would think if there is provision to plug a second battery in while the first one is being replaced is all you would really have to do, after the backups are made, of course. The only reason to have the power on for the switch would be for the dumb systems that don't have provision for the jumper battery.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)