KF's tip is a good one.
I'd try the 9 volt/ 8AA pack and unbolt the ground rather than take a battery lead loose at the battery terminal. A battery ground assuming you can reach it easily is easier to deal with than a battery clamp that is secure and clean with as mine are, coated with a thin layer of di-electric grease to inhibit corrosion.
I've done this while working on vehicles for short term and it works great. It bad enough to re-set radio stations/time, but on the newer cars you have so much electronics it can be a major hassle.

Biggest reason to my thinking is that as KF mentioned is the fuel injector air/fuel ratio. Lose your electronic memory, the computer has to " relearn" the proper mix as you drive, which may or may not be best for fuel consumption and vehicle performance. At the steep cost of gas, who needs that? You also might trigger some computer engine codes that would need clearing or they could cause problems?
I'm thinking one of those dashboard roll-up solar panels that deliver a trickle charge to battery might be the way to go here.
Park so your getting the sun from East to West and I think you could eliminate the worry?
Hard to imagine the battery would go completely dead with that set-up and with your back-up Power Pak, I think you have the bases covered.