Low gas mileage and battery drains after repairs

I had my 2007 prius repaired to pass inspection (new tires at one place, new rear brakes at another place). Since receiving the car back it now is VERY sluggish (especially at speeds above 40 mph). Also the main battery starts at normal then drains down to one bar after the first mile or two and spends the entire highway ride trying to catch back up (it never used to get below 3 bars in this situation).

To add another possible factor: I ran out of gas just before these problems and today I checked the 12volt battery when I start the car in "signal check mode" and it started at 11.3v but as soon as I start the car it instantly gets to 13,9v.

Also I was told by one inspection place that the last third of the muffler (i.e. the third closest to the rear) is leaking and should be repaired soon (but I didn't think this was the issue because it was running perfectly fine before I took it in).

To try to see if it was the brakes I put my hand on the wheel after driving for 20 minutes and it doesn't feel warm (but maybe I should be feeling somewhere else). I just don't know enough to diagnose whether it is the brakes, or the 12v battery, or the new tires misaligned/underinflated (the ride feels very smooth and I can't imagine underinflation causing this much of a drastic drain on the main battery), or the muffler. I had no problems before I got the rear brakes and new tires. Any help would be greatly appreciated.

One more note, when it is struggling to get above 50mph there is a kind of ticking or fan noise that the engine makes (I assumed because it was working so hard and not getting much assistance from the battery).

 

Thank you! 188,000ish.

 

There is the standard yellow check engine light, I had figured it was an oil change light that the oil change people forgot to reset. There's also the low tire pressure light but that one is broken for my car and is always on regardless.

 

Gotcha, I don't have a scanner or anything so I guess I will have to take it in to a garage to get checked and see if the garage can figure it out. It's always a pain to be car-less for a day because of work etc... So I was hoping it was maybe something I could get fixed on the spot (like the 12v battery) but it seems like that wouldn't be causing this much chaos (e.g. causing the main battery to drain down to 1 bar and get bad gas mileage and not be able to go have much acceleration after 40mph). Thanks for the heads up about the check engine light that does make sense now, I truly thought it just came on every 3000ish miles for an oil change (facepalm).