Hybrid Battery Won't Charge Pass Halfway Poor MPG

Bummer! If it was mine, I get the HV battery checked out. It does sound like one or more bad cells. But you don't know for sure what's going on till you test it out.

 

This is one of the symptoms of an aging/degrading hybrid battery. You can read about the warning signs you battery is communicating to you here:
How do I know if my hybrid battery is failing? - Hybrid Automotive

 

My wife's 07 battery was just replaced by Toyota, 2 weeks before the warranty expired. She said her mpg dropped into the low 30s for about two weeks before it threw a code. We've had it back for a week and it drives like new.

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might be the perfect time for a grid charger, if you plan to hang onto it. see post #3.

 

Ok could someone tell me about the grid charger? My 2005 Prius is getting about 42 MPG. I've noticed a big drop in MPG after CO Clean Air emissions made me put a new gas cap on the car just to pass emissions. Could there be a link? The car does have 172,000 on it btw.

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The gas cap shouldn't matter, but you can always put back the old one

 

Unfortunately I threw it away of course

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Ok tell me. How do you get the HV battery checked out? And I've read on this forum before that you can get your HV battery replaced with a recharged battery (so like a used battery?). How much do those run and how do I find a mechanic that will install it? My regular mechanic won't even change the oil in my car because of the HV battery.

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Either take it to a Toyota dealer, to a shop that specializes in hybrids, or diy with a mini vcs and techstream software or a wireless obdii reader and Torque Pro (Android) or Engine Link (iOS). There are countless threads here about these tools. I use the Mini VCS and Techstream, but also have Engine Link on my phone for quick & dirty easy stuff. With either of the smartphone options, you'll need to get the PIDs installed, which is a bit of a pain.

I would never take a Prius to a mechanic that doesn't know how to work on them. Actually, I almost never let anyone else mess with my car.

A used, rebuilt battery is way less than a new one, of course. But it is likely to only last a few weeks or months depending on the quality of the parts and the skill & diligence of the rebuilder. The best option, imho, short of a new battery, is a nearly new used battery taken intact from a wreck. My wife's '07 has the cells from a 2015 that have been transplanted into a gen 2 battery case. I bought it all set up and ready to go and replaced it myself. Not hard at all.

 

The hv battery is a maintenance free item, you don't have to do anything with it. Just drive the car and the car will let you know if there's something wrong in the form of warning lights.

Don't fix it if it's not broken. Many times if you blindly go to shops to fix a non issue, they'll end up breaking your car

 

@jeff652 from Hybrid Automotive is quite active here.

This system is their best option, IMHO.

Prolong® Deluxe Reconditioning Package - Hybrid Automotive

Here is a less expensive, but more labor intensive option.

Prolong® Value Reconditioning Package - Hybrid Automotive