Drastic Fuel Economy Drop

I have a 2005 Prius with over 200,000 miles on it. I did replace the hybrid battery, 4 years ago.

Generally, the car was getting 42-47mpg. I do mostly around town driving where it was getting 42, although I haven’t seen 47 in awhile, even on the highway.

It has suddenly dropped to 37 mph (according to the driver’s screen). And I’m 4 hours away from home. It seems to be running fine and the engine light has not come on. I have changed no driving habits, the only thing that has changed is my mechanic said recently my catalytic converters is bad

When the battery failed the first time I don’t remember the engine light being on. I just remember the fuel economy dropping drastically and boom! Suddenly it was running VERY badly — and the red triangle came on.

I checked my tire pressure. All tires are between 30 and 35 psi.

Is there anything else I should check before I bring it somewhere in a strange town?

Thanks,
Paige

 

After looking at the Fuel Economy questions again I thought I’d add a few things.

Tires: brand new, bought 3 months ago.
Alignment: I am not noticing any pull
Accidents: I did hit a guard rail a month ago, side-swiped it
12V Battery: Replaced 4 years ago, I think (but not sure). The fuse for the hybrid battery went this spring. Before I towed it to my mechanic, I had friends try to jump it.
Oil: Had it changed a month ago and they always check the air filter and it was good.
Brakes: Replaced 2 yrs ago
Computer Screen (?): shows me getting 99mpg when coasting but when I step on the gas it drops down to 25mpg, even when going slow.

 

Is there any way to tell by looking at the computer screen/monitor with the picture of the battery and wheels showing when engine vs battery are being used?

 

I was wrong. I bought 2 new tires. They are Solar 4XS. They are in the front. The rear are Cooper Snow Groove. But again, I’ve had these on for months. Why would they suddenly cause a drastic mpg drop?

 

Thank you all for your input!

On the drive to the dealership, the screen showed the wheels charging on down slopes and the bars went from 6-7. So it was looking pretty good.

Yes, indeed, the cat is bad, which my home mechanic told me about, but also said it would not affect the performance. He also said the cat converter would be very expensive so he didn’t recommend replacing it given the age and mileage. (Over 200,000.

The O2 sensor is also bad. Which the dealer mechanic told me, along with the info which I already knew about the cat. Even if they are wrong and there is more issues. I should hopefully be able to get home w/o it crapping out on me!

Thank you all for your help.