HV Battery Failure Poll

Pearland,Texas which is South of Houston

 

Perhaps you might share what those reactions are?

The reason is I've found adding water restored original capacity. It looks like the weaker terminal seals of the original NHW11 traction batteries are letting the H{2} and O{2} gas escape, eventually dehydrating the cells.

Have you taken any of the Toyota, NiMH batteries apart to directly measure and quantify these 'irreversible' reactions?

Bob Wilson

 

2006 Prius (Gen II)
Hybrid batteries died at 80,500 miles / 3 years, 3 months old
Car is in North Georgia (Northern metro Atlanta area)
Parked in an enclosed garage at home & a covered parking deck at work.

I was very, VERY surprised that the batteries failed so quickly, but was relieved that they were replaced under 100,000 mile warranty at no cost to us. I hope the new batteries last longer than 78,000 miles...

Tom

 

First of all, chemistry is not about seeing things with your naked eye. To see what actually happens, one has to perform an analysis using various techniques like gas chromatography for example. Even the simplest reactions occur in multiple steps and to a very small degree have the side reactions. There are a lot of reactions were the side reactions are so small for all intents and purposes they can be ignored. However in the battery reaction, because the reaction happens back and forth so many times that the effects of the small side reactions become significant. How do I know it affects the car's battery? All of metal hydride batteries have these side reactions, it's the nature of the reaction in the battery. Research papers which study batteries have clearly shown this.

If the reaction was totally reversible and there were in fact no changes inside the battery, if you have the same reactants in the same conditions and you will achieve the same product. So this would cause the battery to last forever without wearing out. So it's no surprise that the battery wears out, this wearing out is due to a chemical change inside the battery. The battery's capacity is depleted as overtime the reactants are chewed up by these side reactions. It's the reason why battery wears out and has less capacity. There simply is less of the right chemicals to perform the almost reversible reaction that happens inside the battery. It is an absolute proven fact that all batteries wear out. A battery that only has 80% of its capacity left has only about 80% of the reactants left inside. The other 20% of the battery contains various chemicals, which can be of thousands of forms with usually one or two dominating that 20%. This is unfortunately the nature of most chemical reactions if not all. Of course we know that the battery the side reactions constitute a smaller fraction of a percent of the total reaction. After all the battery can be charged and recharged thousands of times without significant depletion of the chemical due to side reactions.

What this poll tries to determine is if the climate where the car is driven and stored plays a dominant role in determining battery durability. This will still not determine what is the cause of the battery failure are it's wearing out. Is it the chemistry inside the battery depleted and the chemical in side reactions, or is it corrosion which is also sped up by higher temperatures. From a reaction point of view, research has found that nickel metal hydride batteries have approximately half the lifespan is stored at 35°C versus 25°C. But nevertheless even if stored at 45° C, which is not uncommon in the vehicle with its windows up in sunny and hot climate, could still last the life of the vehicle. It's only the real world where we are going to get a better understanding of the lifespan of these batteries. It could be corrosion that plays a major role.

On the other hand, maybe it's seal failure or other mechanical issues that are in fact responsible for dead batteries. Could be that in fact how rough the road is might determine the lifespan of the battery the most. So in fact car manufacturers should spend more time making the design more robust and less time in the chemistry.

One thing is for sure, the myth that the battery will outlive the car, has already been proven wrong with quite a few batteries starting to fail on the first generation of the vehicle. Maybe the improved design of the second generation will solve that problem, but until the second generation vehicles reached the age of the first, it has still not been proven whether the improved design is actually better or for that matter worse.

 

I've been at a Toyota dealer now for 7 years. From my observation the Prius HV batteries fail for two primary reasons, both of them avoidable. This is not to say they don't occasionally fail for other reasons, just that these are the main reasons.

The first is corrosion, usually brought about by moisture (water) in the trunk area, usually from a water leak like a taillight gasket or body damage from a collision.

The second is cooling failure usually caused by vent blockage either through some object physically blocking the vent intake or lint clogging the intake.

Keep an eye on your spare tire area for moisture and also on your vent intake for lint buildup. Note also there is a little screen available you can put over the vent intake that will cause the lint to collect there so it can easily be cleaned. if the lint collects at the fan itself it can also become clogged but it's more difficult to take apart and clean.

 

according to this poll, we only have one gen 2 failure so far, and it was under warranty. really great news for toyota.

 

Southern California here. Our first Prius, the blue one, had the battery replaced under warranty at 9+ years and 125k miles (we're the original CARB state). As second owners we don't know where the car was parked; we only had the service history. The guess, though, is that it spent a lot of time parked in the hot sun since there was substantial sun damage to the paint, especially on the spoiler.

 

okay, that's two.

 

Is it possible you also request for the mileages on those cars? That would be cool. Maybe, also what time of the year, or something like that, that those batteries failed.

 

I am the current owner of a 2007 Prius Touring model. I purchased it in early 2017 while it was in the early stages of HV battery failure. It had the codes but was still drivable. I have the complete maintenance history since the original owner purchased it. It spent it's entire life in north-east area of Charlotte, NC and had all it's scheduled maintenance performed by two Charlotte area Toyota dealerships. Battery failed at 143,000 miles in Feb 2017. Disassembly and testing of the battery showed one module failure, with 2 additional modules that were weak. I'll update this post later this evening with info pertaining to which module failed and what the capacity tests showed for the other 27.

Update: I added the part above about the two additional weak modules. The three modules were #9, 11 and 13 from the ECU end, this would be Blocks 10, 9 and 8. The weak module in each block was the module closest to the ECU. The failed module in Block 8 was the only one that was unrecoverable. The remaining 27 modules recovered to between 5974 and 6545 mAh, with most around the 6200 range.

 

Failure occurred at 175k miles on my gen 2. I got a direct OEM replacement at that mileage and currently have 65k miles on the new OEM replacement. I didn’t even have to pay for the replacement since I bought it from a small dealer who flips cars. I’ve not had any issues with either battery either. I would recommend for people to get a direct replacement rather than rebuild the battery because you just never know how long the old cells will last.

 

Based on my experience, the main cause of battery failure is loss of capacity. If you allow the loss of capacity below ~ 50%, then the modules will begin to fail.