You probably can go seven days or more easily with the 23, all on ev. At any speed or use the engine won’t kick on if it is in ev mode up to 84 mph, until the battery is depleted. The 23 I bet will be getting 50 miles on ev being reported maybe more. Sounds like you will be wanting to run the engine just to get the oil circulated and run it. Need to use up gas within a year as a fair guess, the Volt would run the engine and burn the gas after a year if the driver didn’t. Another extra a plug in has to think about, but then you can go anywhere anytime without worrying if there is charge to get you somewhere right away. I find the 20 Prime very quiet in ev. It is an ev in ev mode. In your case in Texas there is also extra cost for ev registration, $200? Not sure if they include plug ins, seems like they wouldn’t. So if gas is $4, that's 50 gals in your favor to use the engine.