Possible battery degredation?

I have a 2005 Prius with 91,000 miles. I keep reading online how Toyota says their batteries aren't degrading with cars up to 200,000 miles.

But I believe that mine is wearing out. For example, my 33 mile drive one way to work has me drop in elevation about 1000ft in the last 10 miles. Most of that drop comes in a stretch between miles 22 and 28. The last 5 miles has only about 200 feet of elevation change. (See the attached pdf file.)

In the early days of my drive, the battery would go fully green on the big hills down to work, and I could make it to work still with all bars green.

But now, one new symptom is that the motor starts to run at the bottom of the big hills (there's a light at the bottom that many times I have to stop at). I'll have all bars green, and the motor starts while I'm stopped and sometimes winds up to fairly high RPM. I'm thinking the computer is trying to DEPLETE the state of charge because since capacity is down, it's overcharged.

When I get to work now, it's almost NEVER still fully green. I'm still at the top of the blue, but rarely green.

Finally more to the point, when I leave work, the first 1/2 mile is nearly flat, and yet I fall from the top of the blue to 2-bars purple and the engine is running already charging at a light there where I need to stop at most of the time (even in warm weather where it should could be off except for low state of charge). Yes, I know the car is running hard from start up to warm up the catalytic converter, but when the car was new, it would NEVER do this. This is with air conditioning OFF. It's of course gotten worse now as the weather is getting colder (my trip is between south-west Denver to Boulder in Colorado) and it takes longer for the engine to get to its operating temperature.

There are other symptoms too like decreased gas mileage. Even though I drive better now (I drive now like a hypermiler), I'm down from an average winter tank of 50MPG to about 45MPG (my best tank over the summer a while ago was 58.6 on that hilly drive!!!).

So all that is to say, is it worth the time and maybe money to take my Prius into Toyota and have them look at it? I've only had "official" service on it once (I do my own routine maintenance regularly), before 36,000 miles, and I asked them to do a battery capacity test. I wanted a baseline at that time. But the technicians told me there was no such thing. Hmm....

Anyway, I'd appreciate any suggestions about what to do before I hit the 100,000 mile mark. Are there tests I can do? I read about Toyota doing cell voltage and resistance checks. And maybe there are aftermarket things I can purchase to find that out for myself? (BTW, I'm an electrical engineer so I'm tech savvy.)

Thanks in advance! (From a very happy Prius owner overall).

 

Thanks for getting back with me. I'll be looking for the PM.

I got the elevation through a brute force method that took a long time (boy I wish the Prius GPS had elevations too ). I had wondered for a long time what sorts of elevations I went through every day.

But in playing with Google Earth, I noticed you could click on a location and get its elevation. So I went to GE, and then plotted (using the ruler) every 1/4 mile on my route. I typed in the elevation GE gave me for each point into Excel and plotted it.

However, there's an easier way for your routes that I know now.

Go to Google Pedometer (okay, they won't let me link because I don't have enough posts - but do a Goggle search). Zoom in to the start of your route. Hit start recording, and then click your route. You might have to play with the "Draw Route" radio buttons, as GP tries to be smart about your route, and sometimes you have to do it manually to get what you want. Finally, on the left panel, click on the "small" or "large" Elevation link. It will compute your elevation (be patient if it's a long route).

This is MUCH quicker than the GE method, but the elevation, if your drive is over 8 miles or so, won't all show up at once and you have to use the scroll bar. But if you have a graphics program, you can cut and paste them together. I got pretty close to the same results, but GP can be done in minutes vs. hours the other way.

Hope that helps!

 

There's no doubt that batteries wear down and don't hold as much charge as when they are new. But I'm, to be quite honest, suspicious that when "Toyota says its out-of-warranty battery replacement rate is 0.003 percent—or one out of 40,000 Priuses—for the second generation Prius" (First Numbers on Hybrid Battery Failure | Hybrid Cars) then they aren't doing a relevant test (hence my comment about the technician telling me that there was no battery capacity test). Of course they don't have to replace them if they don't have a metric by which to measure! The low statistic for "out of warranty" replacements says more about the out-of-pocket cost of replacement than having a metric by which to measure them against before the warranty expires.

But, for example, NiMH batteries can have cell reversals and other behaviors where the batteries actually die. And in a stack of 168 cells per car, is it possible that one or more may actually have gone bad? Is it possible that with that many cells, the "good" ones mask the "bad?"

My expectation, to answer your question, is that Toyota warranties the hybrid system for 100K miles. If all I have is normal wear and tear that's fine. But if I have a true, legitimate problem, I'd like to get it fixed before the warranty runs out.

I just want to find out if there is a fair test that can be run to look at the batteries. Does the Prius computer itself monitor battery health and alert the user if it finds a problem? I have a co-worker who had his Honda Insight warn him of a battery problem at about 30K miles. Honda replaced the battery free of charge, and his mileage went up 10MPG pre/post the replacement. Would the Prius warn of a similar problem?

My car, IMO, is showing symptoms that in my mind indicates at best, battery fatigue, and at worst, battery failure. But that's why I'm going out to the great collective of experience and knowledge on PriusChat for advice.

I would appreciate hearing from anyone with answers to my questions or suggestions of where to go from here.

Thanks!

 

So many thoughts, so little time...

First, I was not trying to imply that my Prius is showing more time in the green, but less. And more to the point, when it is in the positive region (5 bars or more), it seems to drop into the negative region much more rapidly.

Just to reiterate, on my drive to work with the big downhill portion about 2/3rds of the way there, my Prius has almost always charged to 8 bars down the hill (from day one). The following 5 miles of gradual downhill, when new, I could finish off to work running nearly 100% on battery (and still arrive with 8 bars).

Now, I rarely get to work with 6 bars, and never 7 or 8. And I'm driving more conservatively than when new.

But on leaving work, in only 1/2 mile, less than 2 minutes of drive time, and only 50 feet of climb (accellerating slowly to 35MPH), I'm down to two bars almost every day. So I've used from 25% to 56% (depending upon uncertainty in the calculation) of the useable battery capacity in that short time & distance.

Second, I've been noticing this trend for a year and a half or so; i.e., through multiple seasons, temperatures, loads, road conditions, etc. I can see temperature effects for sure. Yet the overall trend is still towards muchlower battery capacity (IMO).

Third, (just as a response to recent post on this thread), last February I drove from Denver to Nashville, interstate (75MPH) most of the way. On the way there, I did experience 7-bar green SoC throughout eastern Colorado, Kansas (it averaged below 20F), and into Missouri. But then as temperatures warmed up as I drove to lower elevations and eventually south, the SoC went back to more normal. Gas mileage on that leg of the trip was a little less than I'm used to on the highway, about 40MPG. On the way home, through, through Kansas (again 20F), I only averaged 33MPG. Typically 3 to 4 bars. WAY DOWN on MPG! I did not notice a head wind either driving or when I got out to fill up and for stops. I drove this stretch before in the summer, and both directions got between 42 to 47 MPG. So these out-of-character indications I chalked up to colder temperatures, and probabably some part due to an older battery.

Anyway, thanks for the feedback. As I stated in my 1st post to this thread. I'm not in any way complaining. This car is amazing, and I would buy another in a heartbeat if I had the money and need. I'm just trying to get information about whether my battery is behaving as expected after 90K miles, or is it having a problem that I should take it in for.

So far, the jury is still out in my mind.