Difference in EV mileage between Base and Advanced?

The 2012 has been sitting for 24hrs now without being used or plugged in. Just got 12.5v, 12.3 with lights on and 14.2 turned on.

The 2013 has mismatched tires on it and 3 of them are not high MPG tires. The 2012 has fairly new high MPG tires on it. They may not be the best tires for MPG but they're pretty good. Tires are most likely not the cause. I'm seeing between around 20% difference in EV only. Without EV figured in the equation both cars get virtually the same MPG.

Under normal driving where I'm trying to get the most EV miles but still go with the flow of traffic I get consistently around 13 miles on the 2013 but only 10 on the 2012. Saturday morning I drove down a stretch of road with no traffic and few lights. I was able to squeeze out 15.5 miles from the 2013 and 12.5 from the 2012 until the engine started. I then stopped each car at that point and restarted so that when I got home I'd get a rough idea of what hybrid mileage I got. One came in at 57mpg and the other 56mpg.

I know my methods aren't scientific but there is enough of a difference between them to conclude that there is something that's keeping the 2012 from getting the EV mileage it should get.

Right now I've got 3 Prius, 2004, 2012 and a 2013. I'm going to be selling one of them eventually. The one I know I'm keeping is the 2012. I'd like to find out what's killing the EV mileage and get it fixed but it's not a deal breaker for me. What is frustrating is that there are several trips that we use the car for that if it got that extra 2-3 EV miles then the engine wouldn't have to turn on. Many times it turns on a mile or so before we pull onto our street.

I am pleased to see the discussion about this. Thank you for your thoughts about what this might be.

 

Here are a few answers:
I do have a scan gauge II in my 2004 Prius and Sprinter. I believe I've got a 3rd one around here but the software in them is old. I'd be willing to connect it and run some test but someone's going to have to run me through setting one up again. It's been 6 years since I set these up.
Alignment performed last month
Tires balanced the day after I bought it.

You're right about differences between trips can make a difference and the non-EV part of my test last Saturday was small and far from anything to base conclusions on. However, I did drive both cars for a lot of highway miles on batteries that were not charged so there was no EV miles. Both drives resulted in low 50's mpg. No more than a couple % difference. The EV difference has been consistent wether I'm driving to maximize EV or trying to just drive normally while keeping the engine from coming on. The 2013 always gets significantly more miles in EV percentage wise.

 

Missed that the first time around. I'll try to find a place where I can safely do that without inhibiting traffic.

 

There are no aftermarket accessories on the 2012. Last Saturday's test run was with the windows rolled up, A/C off, no lights and just the radio was on.

I'd love to get this fixed but I'm not so sure it will happen. How many dealerships have someone qualified to run down something like this and fix it? Then, who's going to pay for it? It's a certified used hybrid but there is a deductible for each visit and warranty work is only done when something breaks so this wouldn't be covered unless they happened to find something wrong. If they find nothing I'll be stuck with a large bill and that leads into the economics of it. A few miles per charge doesn't add up to a lot of $$ over the coarse of a year.