As far as saving the presets, there are devices you can get which plug into the cigarette lighter. I think they use a 9-volt battery and a diode. They might not work so well if the cigarette lighter is switched with the ignition.
What I've discovered works well to save presets is a rechargeable 12V spotlight. The one I have, and I would guess most of them, don't have a diode between the DC power input jack and the battery. Probably because it'd have to be a hefty diode for the amount of current that light draws.
Because of that, the rechargeable spotlight will supply 12V to the rest of the car when you disconnect the car battery if it's charged up and plugged into the cigarette lighter. (If your lighter socket is switched, key needs to be ON and you should turn off the radio, fan, etc.)