Main traction battery possibly failing?

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

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

 

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.

 

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.

 

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.

 

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.

 

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?

 

ok. well as far as battery replacement goes, toyota will not replace an HV battery until they have a DTC that indicates a problem with it. if you saw failure symptoms, you'd be seeing a DTC.

one thing you might try if you've got a friend in the local service department is to ask them to do the battery equalization procedure. they do this with used hybrid cars before they get sent back out to the lot. it's in the scantool in either the HV or the battery computer menu.

otherwise, anything about your commute change lately? that's a common one that DH had to explain all the time.

 

What ever happened with this?

I am having the same symptoms. 78K miles; my commute goes up and down lots of hills (live in Denver and commute up and down the foothills). Battery SOC goes up and down *much* faster than when it was new. Many times now I'm at full green at the bottom of hills and the ICE runs to remove overcharge, or down at one line and running fully off the ICE.

Gas mileage per tank is about the same over the last 25k miles, but I've learned how to drive it for better efficiency. Slowly my MPG has increased on the commute from about 47MPG to 52MPH. I can do the full round-trip commute at >57MPG, but it's the little stuff around town that drops the mileage per tank. However, my suspicion is I'd do better if the battery was "new."

I've taken a lot of road trips to with the car, and in February, I came west across Kansas and only got 33MPG. I'm used to much more like 42 on the highway, so that was a noticeable drop. I've driven that stretch twice before and gotten 42MPG or better. I did not notice a wind this trip, either driving or when stopping for fill ups, food, or other stops. So it was weird.

All this is to say, I'm thinking of taking the car in for a "battery capacity test" before the warranty goes away. I was told once by a Toyota mechanic that they don't have such a thing, which both surprises me and doesn't surprise me. It surprises me because it's what should be done (I'm a EE and do satellite work, and battery capacity testing is integral to making sure we have good batteries before sending a satellite into space that *needs* good batteries) to tell how if the cells are behaving properly; but also not surprised because they could end up replacing a lot of batteries that otherwise might "get by."

I feel that Toyota engineers have done a GREAT JOB on their algorithm for controlling the battery state of charge, but at the same time, batteries don't last forever, and I've been skeptical since I bought this car that I would not see significant battery degradation before Toyota wanted to admit something was wrong.

Please don't take that as a negative against Toyota or the Prius. I LOVE the car, and would get another in a heartbeat if I could afford it.

Anyway, all that is bit of a ramble, but back to this thread, what ever happened? Comments anyone?

 

Hi Whiten,

I can see a drop from 5 bars to 2 in cold weather, during the first minute of operation. That is normal. It because I have a small hill to climb, and I forget to take it slow sometimes. The cold start routine of the Prius keeps the engine at reduced power and uses electric drive for the first minute. Thus the dramatic battery change during this time. Especially with cold tires. I actually know the point in the road where the system switches. Because I can push the throttle at that point, and rather than the yellow arrow (discharging), I get a green (charging). This point in the road is only about 1/8 of a mile from the starting point, and reportedly, its 57 seconds from startup.

If you want to baby the battery, then let the car sit for a minute before driving away. This way the cold start routine will be out of the engine low-power time.