[erndog66]

I am looking at the ones with 9V battery that plug into cigar lighter socket. I know I would need to keep the car in the ACC position. I have a small battery jump starter but I would have to connect to the existing cables at the battery and I am concerned it could become disconnected during the change out. Thank you for your suggestion.

I personally didn't like the idea of the ignition being in the accessory position due to additional load on the battery while disconnecting. Not sure how that would even work with push button start actually.

 

[erndog66]

I used a 9V Battery with alligator clips. It maintained the settings while switching out the battery.