2010 Toyota Prius mileage drop

I bought a 2010 Prius new. It now has 220,000 miles on it. The mileage started dropping slowly around 3 years ago. The mileage so far this summer is hovering around 35mpg. There are no warning lights on and I’ve never had any go on. I’m assuming the battery is about done and the gas engine is now doing all the work. The battery seems to be taking a bit longer to charge (according to dash info). The dealer checked it a couple of years ago and said the battery was fine. I don’t know for sure if the battery is ok or not. Never got any info. from visit to Toyota about what the problem might be. They put some fuel cleaner in the take and that’s what they recommended to me. Never changed anything. Any ideas? I’ve changed the oil regularly and have kept the tires inflated and rotated. The tires tread seems fine.

10 year vehicle with 220000 miles on it and seems to operate just fine. Average 35 MPG , I fail to see a major problem here . Of course you may not have Low Rolling Resistance tires anymore , driving patterns have changed over the years or maybe the vehicle is just showing signs of wear and age.

Check out this list of symptoms of a failing hybrid battery. #1 is a drop in MPG. https://www.thehybridgeek.com/hybrid-battery-failure-symptoms/

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Folks come here for issues.
Will see more hybrid questions in future.
10 yr old Toyota needs $3000 battery pack?
Would you spend 3000 on a non hybrid repair?
Since you have no real issue other then mileage drop, is repair required?
You think something is wrong. It’s your car.

Do a search for hybrid battery repair in your area, one near me would charge between $1000 (rebuilt) and $2000 (new) for a battery for your Prius, plus installation. I imagine they would check the old one first.

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Because it is “fine”. Sort of. Batteries accept less charge as they age. If the battery only accepts 80% of the charge as new, the battery is still functional. Toyota may even call it “fine”. But it can’t provide the full service the hybrid system used to get as you posted. So the mpgs decrease. Your assessment is correct.

At 220K miles, you can plunk down the cash for a new battery to get your mpgs back, to what, 45 mpg? If a battery is $2500, is it worth the 1100 gallons of gas to improve your mpgs by 10 miles per gallon?

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2005 Prius w/270000 miles. From go to ~60k miles we averaged >54mpg, w/60+mpg on open freeway. Replaced tires with Michelin from Costco and the mileage dropped to ~50mpg that day. We now get ~40-45mpg (on 5th set of tires).

And since about 100k we burn 1qt oil/600miles

THAT’S really good for the environment, isn’t it?

Not one bit. OTOH, dumping the car before it dies isn’t either. We use it solely for essentially trash runs (moving crud we don’t want to put into our other car like plants, recycle crud, etc.) which means 1qt oil/6-months