Is this supposed to happen

Do you happen to have the heat on when this happens? I've noticed mine gets low right after starting sometimes (typically I was already down to half, and then it lost a little more). I've always assumed it was normal.

 

This is probably related to the warm up cycle, see:

Prius C warm up stages | PriusChat

As I posted over there, I've only recently got a scanguage which I'm watching and trying to get my head around. Can't tell if the explanation for my car's behaviour is that it's a c or if it's because it's an Australian model, but I can tell you it isn't quite behaving the way explained in that thread (which is more or less an exaplantion of the Gen III liftback's warm up stages).

Although mine isn't the same, it's still the case that during the first part of the warm up cycle the engine is running differently - the ignition timing is different, the RPM and engine load is different and it simply is not producing as much power as it normally would, meaning the car draws on the HV battery more and performance is still restricted. At some point the cycle completes and this all changes. You can hear the difference when it does. Sometimes you'll also feel the difference and sometimes it means the car will suddenly start charging the battery, depending on the situation at the time.

 

I have noticed that from time to time after I drive to the grocery store, shop and then leave for home, the C will effectively stay in EV mode (without prompting) and register 99 MPG - regardless of my speed - and stay that way until the battery is pretty well drained. This most often leads to an 8 mile segment (from the store to home) that is in the high 70's or low 80's. I have absolutely no idea why this happens, but it does, and when it does I simply smile and shake my head in wonder!

 

Even here (where it is late Spring), I am going to enter a new warm up cycle every time I jump back in the car. It has to be a really short stop for the car to decide to skip the warm up cycle. The warm up cycle can end up being a lot shorter in these circumstances, but normally it will still exist.

 

Just the opposite for my C4.
Currently, in the mornings I quietly roll out of the garage in EV mode but as soon as I'm outside in the open air the ICE kicks in before I can close the garage door. Come to think of it, during the summer months I used to make it past the bottom of my driveway and onto the surface street before the ICE kicked in. Warm garage vs warm/cold outside tempertures.