Replying to the original post.
I am no expert but my impression is that you do not need to leave the power on for the batteries to save the internal sound bank. Both of my CZ's do not have functioning internal batteries.. so If I leave them unplugged without D batteries they lose their internal bank sounds after a day or so. But with D batteries or with the AC plugged in, they will keep those internal banks.
I also use an iPad editor, CZTouch, for all editing, patch storage and sysex dumps. It is a great program to have and very easy to use. With it, I have no worries about losing patches. B/c of this program I haven't even bothered to by a memory cartridge. What's the point of buying an expensive cartridge, having to replace its internal battery, worry about it getting messed up, etc, when you could save an infinite amount of patches on an iPad. And because I use my CZ for live performing, not in the studio, I could easily use the iPad to load patches on the fly in a live situation.