It can be lower if the battery is constantly trying to charge up. (Which you may or may not see on the screen.)
Make sure to eliminate other possible causes first. Increased use of the a/c, more short hops around town without the car being fully warmed up, accidentally lowered tire pressure, etc. are all causes that are cheap to fix.. Check the small 12v battery, too. That is probably the #1 reason for reduced mpg. At the least the 12v should be replaced every 5 years or so, meaning your 2006 is probably due for a 12v replacement. It's a lot cheaper than immediately jumping to a conclusion that it's the hv battery.
have to disagree here, a weak hv battery will not cause lower mpg. you're fine until you get a dash light/ trouble code. look elsewhere for your mpg problem. has anything changed?
Yes it will. A battery with diminishing capacity will need more frequent charging and it will have less power for ev assist.
he didn't like the question he asked in the first one. otoh, my 95 year old father asks me the same questions all the time.
When my HV battery died on me late December 2015, I was still getting nominal MPGs. Looking at my spreadsheets for the month before I replaced the battery I was getting 40-50 mpgs in the wintertime which is what would be typically expected.
When the HV battery suddenly died a couple months ago, I was still getting pretty good gas mileage (47-52 mpg typical in the early summer). Now, my gas mileage has improved slightly after battery replacement. One thing I definitely noticed is that the state of charge tends to stay rock solid most of the time at the middle of the blue range.
We experienced the same thing with our previous Prius. MPG was fine and normal until one day the entire warning system lit up. The dealer confirmed that it was the hv battery and Toyota replaced it for free. The failing hv battery did not lower the MPG. As I stated earlier, there are other common reasons for MPG to drop that are easy and relatively cheap to fix. At a reasonable 5 years of life per battery his 2006 is due for a new 12v. The 12v is a most notorious MPG dropper when it starts to go.
