EV button and its effect on the HV battery

I made a comment in another thread about he EV button which subsequently was replied to. The subsequent discussion was taking the thread off-topic, however I found it interesting and worth further discussion.

So I have cut and pasted the relevant posts here so the discussion can continue.

First the original comment and my reply that started it all off:

 

While I agree that the Prius does a good job of protecting itself against stupid, in the long term, killing your HV is exactly what will happen. By constantly forcing long full to empty to full (80%-40%-80) duty cycles you will cause the HV battery to fail sooner. There are only a finite number of charge/discharge cycles in the life of a battery.

If you do what you say on an infrequent basis, it is probably no worse than what the car would do anyway, and wasn't point of my post, which was in the second paragraph.

At the end of the day, it is your car, you can do what you want with it. Come back and let us know at what milage you had to replace your HV.

 

Please explain why the HV battery has to be replaced at a higher rate on the older (by age, not model year) Prii, if they last forever?

A new healthy battery will not necessarily have this problem which is caused by self-discharge. Even if the new battery self-discharges to 0 volts, it will happily sit like that indefinitely (in a controlled environment). When it is time to use the battery, just fully charge and it is good to go.

Please tell us the process to rejuvenate.

Yup, I did.

I'm sure you are very knowledgable, but pretty sure the Toyota training about NiMH is limited to what you need to know to work on Hybrids and does not necessarily make you an expert on the subject. However, I come here to learn, so hope there is some substance to your training that you can pass on. I'm all ears.

I am aware the the HV battery management software restricts the battery to 40%-80% as it was found in doing this the effective charge/discharge cycles were exponentially increased, hence having a real benefit in longevity of the battery (which has been proven in the field). However, the battery will eventually wear out and need to be replaced at some point. I am keen for you to expound on your theory that the battery will last forever, which you imply by your statement about what kills the NiMH battery:

While these things are some of the reasons a battery will fail, it really is that these factors will speed up the process of failure. All batteries will die eventually.

This will more likely happen in a used battery that has become out of balance. Caused by self-discharge to the point where one or more cells within the module becomes reversed. A module with a reversed cell can never be revived and will cause a DTC to be thrown

 

Yes, it is good for the battery to be used, it keeps it in good condition. I never said for the car not to be driven, so where does your question come from?

 

Wow!

Just wow.

 

I was saying not to use the EV button (a DIY accessory, not standard fit on the North American Gen II) to force the car into EV.

If the car is happy to use EV to propel the car, then let it. It knows what it's doing, just don't force is all.

 

Incidentally, you are not gliding if you are using any of the motors. Gliding is where there are no power arrows anywhere on the Energy Monitor screen.

 

You are obviously using different terminology, I have never read where this distinction is made.

I have always understood what you are calling coasting is gliding and what you call gliding is pulsing, it makes no difference whether you use the ICE or the electric motor to pulse.

 

That is an interesting take where he seems to have made it up as he went along.

The concept of pulse & glide is not a hybrid specific one so the basic concept is pulse up to speed (say 35 mph) and then come off the accelerator, move to neutral and glide until you reach the lower speed (say 28 mph), put it back into gear, rinse and repeat.

I'm not sure why he wants to complicate things by calling pulsing under electric gliding, when gliding and coasting are the same.

I agree in principle to most of what he's says, but my biggest problem is that he kinda infers that the Prius magically generates free energy from pulsing on electric (what he calls gliding) and regenerating free energy by regenerative braking.

This is simply not the case, there is no free lunch. All energy in a Prius Hybrid is generated by burning fuel. End of story. The biggest inefficiencies are converting energy from one form to another. Therefore it is inherently less economical to use electricity to power your car in the pulse than it is just to accelerate using the ICE.

I believe that if you just simplify it to a straight pulse and glide without any due care whether you use the ICE or electric (let the car work it out itself) you will get much better results.

Here are two better videos (IMO):

Toyota Prius Pulse and Glide Fuel Economy Tutorial | EcoModder

Prius Maximise Fuel Economy Secrets | Green Power Videos

The second one is in a Gen III but apart from the references to the HSI, it pretty much is transferable. You will notice that in both of these videos they do not reference a preference for using electric to pulse. Also note that "coast" and "glide" are the same thing–no energy flows.

See how you get on.