About to cry ... '05 Prius battery died ...

:cheer2::cheer2::cheer2:

 

I dont know Jim. I think that the 12V relation to MPG is a little bit overblown here. My 12V battery is thoroughly ready for replacement. It's over 5 years old and only measures 12.2V, dropping to about 11.8 at IG-on. It was somewhat better (12.4/12.1 volts) until about 4 months ago when I nearly ran it fully down on a camping trip back in May.

Guess what? I haven't noticed any drop in MPG at all. It's running as always at about 55 MPG full tank average and the last two tanks have been even a little better than normal at about 57 MPG.

It's only certain types of fault that would make the 12V battery absorb lots of power and hence waste HV battery power and reduce MPG. Many cases of normal battery aging will just result in higher battery resistance and less capability to supply large current bursts. Eventually it will get bad enough to not boot the computer correctly and you might end up with all sorts of weird errors states as a result, but until that time I don't see any reason why it will necessarily result in worse MPG.

Also if you check through these forums you'll find that "change the 12V battery" has become a bit of a mantra, with every case of poor MPG being told to do this. If you really search through these post however you’ll find that it almost never actually fixes the problem. I counted one post out of about 12 where it actually worked, and in truth I think that one post was actually where the theory was originally hatched in the first place. That is, it was the one case which supposedly “proved” the theory in general.

Now a more capable HV battery on the other hand. I can easily see how that could give a 10% MPG boost in many circumstances.

 

It is true that the increased MPG could be due to other factors. (Resetting the CPUs, New 12v battery, 'New' HV battery, terminal corrosion, etc.) It is also true that not all failure modes of a 12v battery will cause a MPG decline, some just die one morning, some work correctly until all the chemistry is exhausted. The 'one failed cell' mode, is the one I suspect of reducing MPGs.

I am reluctant to suggest putting the old 12 v battery back, to check. Her car works now, more messing with it will just increase the odds of breaking it again.

 

Yeah it's definitely not worth changing the battery back once the job's done.

I'm going to be putting in a new 12V battery before next winter (it's only just spring here now so I've got some time). Interestingly I've just been checking online and I can get the elearnaid optimo shipped to Australia (complete with adaptor kit) for less than I can buy the battery alone locally.

 

I can understand your skepticism. However, if you read back through those posts where a new 12v is recommended, the vehicle usually has at least a 4yr old 12v, or has a documented case of running the battery down. Under those circumstances it would seem to be a prudent measure for multiple reasons, not just the mileage concern, that's why it gets recommended.

At least this story has a reasonably happy ending!

 

Good Resolution.

The Serpents Egg?

You realize your Prius now has a taste for blood?

Pleasant dreams.

 

Yes I agree that it's prudent to change the 12V battery under those circumstances. Like I said above, I'll be changing mine within the next six months even though I'm not having any problems yet.

My comments above weren't really directed just towards this thread, it was something I'd been meaning to post about for a while. That is that the "change the 12V batt" has started to become a bit of a mantra here for all cases of markedly reduced MPG, but if you read through the all cases you'll find very few where it actually sovled the problem.

 

The pendulum swings too far some times, we had a group of owners having 12 volt battery issues, because all our prior experience taught us was when the 12 volt battery was to weak to turn a starter. Since the Prius 12 volt battery never does, we were missing it as a cause for some problems. Now we may be diagnosing too often. The problem is, whether the Prius is your first car, or you have been driving for 70 years, your experience does not lead you to recognizing this issue, so we may well have been stressing it too often, I cannot say.

 

Did you ask what Re-Involt did? Was it as simple as a bad HV battery cell? A modle was replaced?