PRIUS 2007 RUNS MORE ON ICE, AND HAS GOT ONLY 25MPG

Possibly, but you need to read the DTC(s) that the ECUs have logged. Anything else is just a crap shoot that could have you unnecessarily replacing parts that are not the problem.

 

I am somewhat confused, do you have a 2007 or a 2010 or both?
There are 3 main batteries in a Prius.
The Fob battery does not cause mileage issues if it fails, you just can't get in the car. (About $2USD)
The 12 volt battery can reduce mileage as it fails although rarely more than 5 MPG. at 9 years, it could be on it's last legs. (About $200USD)
The Hybrid battery is usually long lived, only about 5% of 2007s have failed yet. ($3500 USD)

 

welcome! makes sense, but you should have a dtc if it's the hybrid battery.

 

Do all the dashboard lights (except the master caution - Red triangle with the ! in the middle) come on if you press the START button once with your foot off the brake?

 

yes, at least for warranty. i don't recall reading about anyone with a bad battery, who didn't get the red triangle of death.

 

there can be many causes for reduced mpg. what would you say you typically were averaging before the reduction?

 

have you noticed any erratic behavior in the battery meter?

 

generally speaking, when the battery is going south, before the triangle of death, the meter fluctuates rapidly from low to high to low, etc.

 

so how to explain 25 mpg, or engine running too much? has anything changed recently? tires? driving area? oil? gas? maintenance? accident?