If you say so ,so be it but I recall when I disconnected the ground lead off one battery ,I don't recall which one the under hood light went out. That tells me no juice
It's been awhile since I've disconnected batteries so perhaps I'm missing something. So In addition why is it when individuals delete a battery why do they have to tie in the other one? Or something like that
Aah, if that is the case, it is possible you have one battery that is completely toast (broke an internal connection or something). If that is the case, and you disconnect the good one first, you could loose power.
If you are worried about it, and don't want to spend any money, do what I'd do: I'd grab my jumper cables and hook them to the junction block (by the power steering pump) and then to another vehicle. Then feel free to replace both batteries without worrying about loss of power.
The reason people need to leave the battery wires connected when they remove one battery is because some power feeds off one battery, and some off another. They are normally connected in the junction block, so one battery will run the truck so long as the cables are there. But cut the cables, and some things could stop working. This was more true on the older trucks (like my '82). I don't think there would be any problem cutting off the passenger battery cables on an '03-'07 truck, but I'd have to look closer before I did it.
Good luck with your swap. Personally, I'd feel better with my accessories getting a full 12 volts from the jumper cables than the 9V from the "setting saver". Just my $0.02.