Battery/Electric smell in 2006 Prius w/75k

I noticed an electrical smell this evening after returning to the car to leave a friend's house. Prior, we drove it for about 20 miles and then it was parked for ~3 hours. Nothing out of the ordinary or harsh about the 20 mile trip.

The smell wasn't a burning, more like a toasted electric device from plugging in too high a voltage as a kid (not that I have experience with that...). I noticed it primarily from the rear vent, but the entire cabin smelled pretty thick of it when we first opened it, prior to turning the car on. I didn't smell it at all from the outside/under the car, so I don't suspect the exhaust.

I noticed it off and on while driving, especially when accelerating hard. The vent fan came on surprisingly early, too, considering it was 45 outside. I also noticed that it wouldn't switch to EV mode, but perhaps that's due to the relatively short trip.

I'm disturbed by the smell as I've not experienced it before and the car is going on 75k. Most of the posts I've seen on here deal with new car smell. Anyone have any ideas? I'm hesitant to talk to my dealer based on previous experience.

 

Thanks for the advice Patrick. I came across mention of the electric heating coils, I'm surprised I hadn't heard about them before.

I haven't smelled it since, so I'm guessing that I just happened to be at a high enough SOC that the coils were used at that point (full green when we started the car), so it sounds like a good explanation (I hope so, anyway!).

I appreciate the help! Hopefully the car will go strong for at least another 125k