Cut off switch for battery in the rear of the car ?

just add wire:

ref=asc_df_B007O0BBFM

sometimes, when you disconnect the 12v, you lose radio presets, or auto window function. you can fix that by holding the window switch all the way down, then all the way up.
some complain that you lose computer learning, and mpg's go down for awhile, then come back with driving, and others that the car won't start, and you have to hold the power button down until it does, or press it 3 times.
it's random though, i'm not sure why.

 

For a Gen 3, you can just pop the hood and unplug the fat white wire in the underhood fuse box; that's the same as disconnecting the battery.

As with disconnecting the battery, there will be things like the clock, radio presets, etc., that have to be reset. The engine may run poorly for a while after you restart (sometimes poorly enough to make a transmission clatter that sounds awful) until it relearns its parameters. If you have the advanced parking guidance, you'll see an "initializing" message until you turn the steering fully left and fully right on flat ground.

In earlier generations, the power windows would forget where up is, and you'd have to reset those. Gen 3 windows are supposed to remember, but it seems maybe sometimes they don't.

As a compromise, maybe look into pulling the short pin that Georgina described:

D/C cut, short pin dome fuse | PriusChat

It doesn't cut all power to the car, but some of the things most responsible for battery drain when off. Maybe there are fewer things to relearn after (but I've never tried it, or studied the wiring closely enough to be sure).

 

or just put it on a maintainer if you have a garage

 

In your shoes I'd probably do the solar trickle charge.

I already do that x2 for a backup generator and a lawn tractor, they both have Prius-sized 12v batteries and sit a long time between starts and it's been working great.