Just to confirm that BillyJack is correct. Been there, done that. Get that radio code prior and write it down somewhere.

 

the multimeter isn't likely to be a help. you need to have a battery load test at most aftermarket car parts counters for free.
but it sounds more like a bad connection between the starter and battery or bad starter solenoid. the dealer will see that only if it fails and momentary not that easy unless its a bad connection, which will certainly be an intermittent problem. my guess its at the starter rather than solenoid if its not the solenoid. you can check the connections at the starter yourself; if the connector wiggles tighten it.
good luck.
one would think the dealer would have found that but they probably only hooked OBD II tester and didn't see anything - guess why.

 

Be careful with some of those load testers. I had an occasion to take a battery in for warranty and the guy said "when did you buy this battery?". I gave him the date and the test came back that the battery was good. I looked at the tester and said how can you load test with a tester that has those thin cables? I had him rerun the test only I subtracted 3 years for the sale date and the thing now said that the battery was bad. We ran the test a total of 5 times each with a different install date and determined that the results were based on installation date and battery voltage, not an actual load test. So some places the tester that they use is not an actual load test at all. I turned the headlights on for about 20 minutes and ran the battery down Then had him run the test again. It finally failed so he had a print out that said it was bad with the correct date. I got a new warranty battery.

I'm not saying all places are like this but some sure are.

 

There was a similar thread about some defective 2015 Fit batteries. My battery failed 3 times and finally, I was able to get the dealer to replace the battery. Since then, I haven't had any problems (knock on wood) with the battery despite even colder Chicago winter temperatures.

One time I left the driver's overhead light on, so I'm also very careful to make sure that I don't leave any overhead lights on when I shut off and lock the car.

 

Same here. No problems since the battery was replaced. I run a subwoofer and Scangauge. I'm just a bit south of you FitIam. Do you ever notice your engine revving on the real cold days shifting into drive (if you have a CVT)?