MPG Slipping - Is It The Battery?

This is one of the first signs of an aging battery, and easily reversible. You can get all of those MPGs back with a little maintenance to the battery:
Prolong Battery Systems FAQ - Hybrid Automotive

 

it's probably not the battery. how many miles on her?
there are several components to the prius, which can cause mpg reduction. unfortunately, it's a trial and error guessing game.
it could be your tires, 12 volt, throttle body/maf, egr, intake manifold, spark plugs, injectors, and more.

 

I just cleared 150 k miles on our 2010 Prius II. I have cleaned the intake manifold, replaced the egr valve and cooler, changed spark plugs, used fuel injector cleaner, done engine flush, etc.

As @bisco said there are many factors at play.

I also had @jeff652 install a discharge ready wiring harness for battery maintenance, and have done 1 charging top up. Saw a slight improvement in mpg, but the HV battery seems to be maintaining a charge longer (able to sit and creep in traffic longer without the engine kicking on).

Now just waiting for a nice box to arrive in early April so I can do even more battery maintenance .

Keep us posted.

 

^ All of the above. Could even be a change in your driving conditions.

How many miles on it btw?

 

In the US, the Gen 4 Trim Two have the same battery modules ad Gen 2 & 3, I believe. The other Trim levels have a Li-ion battery similar to the Plugin Prius, but the chemistry may be different.
I do not believe there is enough data on PiP or the newer Gen 4 batteries to make any reasonable determination.

 

Well the same chemisty, but the pack is not identical. I would suspect they're all improved over 3rd gen, just due to more time and research.

And as far as mpg, the 4th gen's are delivering tiresomely easy higher mpg, at least 10% reported here, fuelly, etcetera.

 

Somebody here found the modules are interchangeable. I am really waiting for summer to see what my mileage will be. I have only had the car since October.

 

Understanding a bit better, @djlen no longer has the 2011, might be shopping for a new one. Missed that.

 

unless you have a defective cell, the hybrid battery doesn't normally deteriorate in the first 150,000 miles or so to the point where fuel economy noticeable. battery technology is improving in many ways, but gen 3 longevity is fine in most cases.

 

we're still wondering how many miles it had.

 

Although it is possible that it is the battery degradation that is causing the low mpg it is very unlikely.

Testing performed by Consumer Reports the Department of Energy and other organizations have shown that Prius is surprisingly unaffected by even dramatic degradation in the battery.

Some of the tests are reported here and indicate that even when the battery declined to less than 40% of its original capacity the fuel consumption was only affect by 3.2mpg.

BU-1002a: Hybrid Electric Vehicles and the Battery – Battery University

I had a Prius Gen 2 and recorded all fill-ups and mileage for the 61/2 years I had it. At 67,000 miles the fuel consumption had improved from ~50mpg to ~53mpg.

A friend still has their 2006 Prius and it is still giving 50mpg after 10 years, I don't know the mileage.

kevin

 

DO note that the Prius DOES NOT run on the battery (unless it's a plugin). The battery is just there to supplement the engine, allowing it to be run in its' most efficient manner. Sometimes you will notice the Prius running on the battery. This IS NOT an efficient mode of operation, and is avoided unless the battery has "to much charge". This is why a degrading battery has little effect on mileage. A failed battery will give you perfect mileage, the car won't run so no fuel will be burned, but it can still move (downhill).

In the US most models of the gen 4 have a different battery, a lithium one. It's actually smaller than the NiMH unit capacity wise, but lithium batteries are more efficient at charge/discharge (I'm told) so it's "better". As Mendal posted, the gen 4 seems to be about 10% better mileage wise than the gen 3 (which was about 10% better than the gen 2). Incremental improvements.

As posted above, there are many reasons the -engine- will run less efficiently. Some maintenance would probably have corrected the lower mileage. The systems in the engine that require attention are mentioned in the posts above.

I don't think you have to avoid another Prius because of the battery. In fact, if you got a Prime (2nd gen PIP) you would see incredible mileage. Check the posts in the Prime section. Again, incremental improvements.

 

10% mininum. I wouldn't mind so much, but those 4th gen buggers are getting those numbers with the AC blasting, driving like it's stolen.

 

The Trim Two has the older technology. All other US trims have the newer design.
Toyota says the newer battery can have issues in extremely cold weather.

 

'much improved' is a marketing term salesmen love to throw around. we won't know that for 10 years, as far as degradation and longevity are concerned. it is possible that they are improved to help provide better fuel efficiency.
as far as your old car is concerned, if you bought it new, 62,000 miles is very early to see mpg drop due to battery or engine problems, unless you got some bad gas or something.
it was more likely a tire or brake issue, or something like that.

 

Our 2008 Prius with about 135K miles (if I remember right) dropped into the mid 30's mpgs. I immediately suspected the traction battery, bought an OBDII Bluetooth adapter and ran a bunch of tests showing the battery was fine.

One day, after two or three tanks of gas while only getting 36-38 mpg, I dumped about 1/2 a can of SeaFoam into the gas tank and the mileage jumped back to the above 45 mpg range. Give it a try. Can't hurt. It must have been dirty injectors. It took me a while to realize it was the ICE, not the EV part that was killing the mileage.

We sold the car with 163K miles, zero problems with the car. We never even had to replace the brakes. The person driving it now has put on another 5K miles so far with zero issues. We bought a new 2015 but the mpgs are still in the 48 mpg range most of the time. It was a little disappointing because I could hit 48 mpg in the 2008 even with all those miles and years on it.

As for me I'm keeping an eye on the Kia Niro to see if it holds up to the promises. I like the interior of the Niro much more than the 2016+ Prius. Toyota is doing things to push me away.