Main traction battery possibly failing?

[dgw]

I bet that someone here has the experience to tell me what a failing battery would behave/look like.
I have 52K miles over 3 years and have been noticing that the battery now fills up (all green) easier and faster than before, and also depletes (down to 3 or 2 bars remaining) faster than ever before. Also, my mileage has been decreasing noticeably although not drastically, even though I drive slower than ever on the freeway (down from 65-70 avg to 60 avg) and have gotten pretty good at maximizing mileage, having driven Prii for 4 years and 75K miles.
Is this consistent with a NiMH battery starting to lose its ability to recharge? If the battery is failing, at what point would Toyota consider it a warranty issue?
Thanks to all, for the collective wisdom I have gotten from this forum over the years.

[efusco]

Dramatic swings in the battery SOC can be a symptom of battery failure. But typically this starts to become evident over a pretty short time period and the swings are, indeed, dramatic usually dropping quickly from green to pink in a matter of minutes.

Since you have a lot of time behind the wheel I'm inclined to think that there may, indeed, be a problem. Now, I'm not sure if Toyota can/would help yet or not. I think that if you know your service dept. well and/or the hybrid tech that usually works on your car that it would be worth while to take the car by and ask them to take a look. I would think that the hand-held tester could look at the battery voltages and such to determine if it has been 'behaving badly'.

[paprius4030]

<div class='quotetop'>QUOTE(efusco @ Nov 1 2007, 01:15 PM) [snapback]533444[/snapback]</div>

Dramatic swings in the battery SOC can be a symptom of battery failure. But typically this starts to become evident over a pretty short time period and the swings are, indeed, dramatic usually dropping quickly from green to pink in a matter of minutes.

Since you have a lot of time behind the wheel I'm inclined to think that there may, indeed, be a problem. Now, I'm not sure if Toyota can/would help yet or not. I think that if you know your service dept. well and/or the hybrid tech that usually works on your car that it would be worth while to take the car by and ask them to take a look. I would think that the hand-held tester could look at the battery voltages and such to determine if it has been 'behaving badly'.
[/b]

This is why it's good to bring your Prius tech a coffee and bagel every now and then

[David Beale]

The THHT can tell if any module is failing. They may want to charge you to look unless the car is complaining (MIL or CE light on) or unless they find the battery is indeed going bad. The car will throw a light once the battery gets bad enough. At least, some of the time.

It's not just because the outside temp is falling? With use, the battery can accept/deliver power faster. Though this usually is seen after a few months rather than years of use.

[usbseawolf2000]

Toyota defines the end of life for the HV battery pack when the capacity falls below 80% of the original.

Falling MPG could be due to other causes, such as engine air filter.

[eestlane]

Most of us on this forum seem to forget that the traction battery contributes very little to the energy used in fairly level ground freeway driving. Most all of the fuel savings is due to the Atkinson cycle gasoline engine. The battery and electric motors are used mostly to get the car moving, since the Atkinson engine has poor torque from start-up. Of course, some savings are contributed by the occasional use of brakes and the consequent regeneration. So, to understand the loss of gas mileage in freeway driving, look for other reasons besides the traction NMH battery.

[efusco]

<div class='quotetop'>QUOTE(eestlane @ Nov 1 2007, 02:35 PM) [snapback]533513[/snapback]</div>

Most of us on this forum seem to forget that the traction battery contributes very little to the energy used in fairly level ground freeway driving. Most all of the fuel savings is due to the Atkinson cycle gasoline engine. The battery and electric motors are used mostly to get the car moving, since the Atkinson engine has poor torque from start-up. Of course, some savings are contributed by the occasional use of brakes and the consequent regeneration. So, to understand the loss of gas mileage in freeway driving, look for other reasons besides the traction NMH battery. [/b]

While I would normally agree with you if the OP had said that the only reason he was concerned about the HV bat was b/c of the dropping MPG when that data is combined with his (admittedly vague) description of the battery SOC display behavior there is cause for concern.

I grant that the cooler weather may be the cause of all this, but a driver with 4 years of experience with the Prius should be familiar with the seasonal/temperture variations and normal battery SOC behavior and if he's noting a pattern I'm going to presume, for the time being, that there may be an issue, esp. since the few well reported cases of battery failure that I've heard report the dramatic swings in SOC just prior to full out failure.

Also, while the main job of the battery is what you describe it also acts as a buffer for energy even at steady state highway driving...an alteration in that buffering ability could account for a small but measurable change in FE on the highway and a moderate to significant drop in FE under rural/city conditions.

[eestlane]

Dr. Evan, I yield to your (as usual) astute and well thought out analysis. A failing traction battery may well cause the system to try to charge it, with less than normal results, resulting in an increased load on the ICE and consequently lower gas mileage.

[galaxee]

well, the OP does not mention maintenance done to his vehicle. dgw, let's talk about other possibilities first. what kind of maintenance has your car gotten so far?

[dgw]

<div class='quotetop'>QUOTE(efusco @ Nov 1 2007, 01:15 PM) [snapback]533444[/snapback]</div>

Dramatic swings in the battery SOC can be a symptom of battery failure. But typically this starts to become evident over a pretty short time period and the swings are, indeed, dramatic usually dropping quickly from green to pink in a matter of minutes.
[/b]

My experience is that on first start of the day, when the battery is cold, the swing from top to bottom can happen really fast, like seconds. But not always. The onset of colder weather (although we're talking San Francisco bay "cold") seems to amplify the effect somewhat. One example I can give was this spring at Yosemite, parked for the night the battery was fully green at 65 degrees. It was just below freezing the next morning and climbing out of the valley, the charge dropped from green to 2 bars in less time than it takes to type this sentence.