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Discussion Starter · #1 ·
2015 Hyundai Sonata Hybrid
178000 miles, runs great but gas milage is starting to bother me. When I first bought the car 3 years ago, I was averaging around 40-50 MPG. Now I can barely reach 35MPG. I See some newer non-hybrid cars getting that kind of milage now. I am Wanting to find info on how to, or who can recondition the hybrid battery, but very little info on Kia/Hyundai hybrid battery reconditioning is available. I Went to and called several Hybrid Repair shops, and I was told they would not be able to help and suggested to replace rather than to service it. So now I come to you here. Does anyone know or have any ideas or info on if and how this battery service can be done? Or should I just consider replacement?
 

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Hold on, are you sure it is the hybrid battery? I'd suggest start with small things.
  • Is driving condition/style the same? Do you have more city drive now compare to before? That hit gas mileage hard. Is your tire pressure at recommend value?
  • Have you checked your engine air filter? Mass air flow sensor?
  • What kind of gas you are using? Lowest price 87 gas could make a lot of carbon deposit when mileage go high.
  • Is your brake/bearing in good condition? Have you accidentally tap the brake and drag it along while driving?
  • Is the 12v battery in good condition? Bad 12v battery will prompt engine running more time to charge them
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I would consider hybrid battery issue in the last. It has 10 year warranty, few people report battery failure and normal degradation won't affect MPG much. Also a faulty battery will trigger some kind of warning light, which you don't have.
I'd suggest you go having a multipoint check with code scan first and ask mechanic to check any issue that could lead to fuel economy lost. A good battery won't pull 15 MPG up.

For hybrid battery, refurished/rebuild is recondition. They pull the bad cell out and swap with some old cell from spared battery pack. They could cost thousands and I'm not sure how long they would last. No experience on that...
 

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Discussion Starter · #3 ·
Thank you for the response Frank,
As for driving habit, it has always been about the same. I bought the vehicle because I drive 26 miles to work 1-way M-F. After doing that drive for 3 years in a GMC Sierra, it was a rewarding decision. The drive to and from work has always been the same, other than when there are changes in the routine, which is not often.
I have regularly been taking the vehicle to get the oil changed and serviced. I also have the preventative maintenance performed such as I had the 100K mile service done, and then the 150K service done.
I believe the brakes and tires are checked every time I get the oil changed, because they say they look good. I replaced the original tires at 130K'ish miles with new energy efficient gas saver tires. Because of the great gas milage I get, or at least used to, I am able to use 93 Octane.
The 12v battery was replaced with a brand new one when I bought the car.
As I mentioned before, I did take the vehicle to several "Hybrid Shops", one of them hooked up an advanced diagnostic tool, that looked like a Heavy Duty 10" Tablet, that seemed to show information for each battery cell, and a few other diagnostic things about the vehicle. After about 20 minutes of testing while the car was running, he mentioned that a couple of the cells seemed to be at a lower charge level and hotter than the rest. He also mentioned that he tried to run a test on the battery, but that the software he had was not equipped for Hyundai vehicles. That is the same shop that mentioned they could replace the battery as an option rather than trying to figure out how to service it. After researching these batteries, there are a couple of companies sell complete units for around $2000-$3000. So if there was an issue with another part of the vehicle, I wonder if it would have, or did, show up on his scanner.
I Hope this helped to explain my concern and my attempt/request to find a solution.
 

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I am no mechanic - but one thing I would suggest before the battery issue would be to have the throttle plate cleaned if it has not been done. That would affect mileage - I have a 2012 sonata hybrid since 2014 and 60,000 miles and have not experienced a drop like yours in mileage during the warmer weather
 
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