New HV Battery in my 2006 Prius, No change in MPG

What makes you think that you should see ANY difference ?

Unless you rode the old battery into the ground.......you probably won't get any improvement.

 

Define "new".

 

That's not new. That's new to you and a totally different meaning. You personally pulled it and can verify the year/mileage?

 

OK. Loss of mpg's may be heat related then.

Also, give it a few tanks to see if it improves.

 

Based upon?????

Display reading, pencil & paper math, distance to "fill" the tank, what?????

 

Well documented as unreliable measure at best.

 

Because the old battery would have to get VERY sick first to cause an observed LOSS of mileage.
The battery only helps with the overall efficiency a little bit; not as much as you might think.

 

Because of what KIND of "performance" drop......and how much ??

 

please don't take this personal, but consider one other thing. my carpool partner can barely get 40 MPG in his 2008. That's just the way he drives. He can't change his bad habits. He gets angry & floors it. He leaves a red light and he guns it. He sees a stop sign or red light 250 yards away & doesn't slow down or coast one bit, prior to reaching it. He doesn't give himself an extra 15 minutes to get where he needs to go.
You can do an experiment. Put somebody in the driver's seat that you know - that regularly gets over 60 MPG. If they can do it, anybody else can do it, except people who refuse to drive in a more normal manner. Just something to consider, that it doesn't have to necessarily have be the automobile.
.

 

Hi Carlos. While it's true that you might get better fuel efficiency with a newer battery that has better capacity, the reality is that this improvement might be too small to notice.

I'm also in the position of having a old worn battery (original battery in 2005 Prius at 305,000 km). My battery capacity has declined quite noticeably over the years, but to be honest my fuel economy has hardly declined at all.

The reason is simple, most of the time the battery just doesn't do very deep cycles, so the point is moot. For sure if your battery capacity is reduced then sometimes you are going to miss out on capturing some regenerative energy, simply because the battery doesn't have the capacity to capture it so it instead gets dumped. However if you look at how often this happens then it's probably only one or two percent of the time that you're driving.

So (depending on the terrain) you might get a 20 or 30 percent improvement in fuel economy, but only during about one or two percent of your journey. And if you crunch the numbers on that it comes out as about two tenths of bugger all.

 

My gen 2 with 205k is showing about 1.5 to 2mpg less on the dash during this last month of hot weather....I don't calculate it by hand but when I did it got between 42-43.

Had a gen 3 that I sold that was getting 39.5mpg and my guess is the high mileage engine had the most to do with it..not sure though.

 

And consider this. Even a brand spanking new battery only uses a fairly narrow part of the middle of its state of charge (40%, iirc -- 40% low end and 80% high end). Most of the time, that new battery stays inside the center of that 40% and almost never goes from one extreme to the other. If the cells get out of balance enough to see rapid changes in the SOC indicator in the MFD, the amount of available capacity may be, for example, 20-30% of full capacity rather than 40%, so the battery is still helping quite a bit because even a new battery rarely wanders outside the middle of the SOC range.