Thank you very much for the chart and the help with this issue. I ordered the battery on 7/30 right after reviewing the chart and just received the call that the battery is in and ready for me to pick up. Hoping to have time this weekend to install it and then I'll rerun the test.

 

A follow-up test would be greatly appreciated. The GMs have a secondary issue with data rate, so the usual hard rules of voltage deviations don't always apply, but with a long-ish constant current discharge, the skew from the data rate can be minimized.

 

Thank you S Keith for putting this up! I can definitely confirm this is the case. I've been rebuilding battery packs since 2014, I rebuilt my first GM 2 mode pack in 2016. I can say from my experience that once these packs are bad it is very difficult to rebuild, I eventually realized it was a complete waste of time. Most of these were near or past 200 K miles, which is typical for the NiMH modules. From what I have read, the Prius is very soft on its battery and they programmed the limits conservatively so that it doesn't pull too much current, also It will tolerate more deviation. Normally a Prius pack I can do one load test of the entire pack, and identify which modules are weak, Replace those, balance, discharge test, and that's normally it. On the two mode packs, I did the same procedure except when I did the second discharge test, I would find one or two more modules that were weak. I would replace those, repeat the procedure, and find One or two more that were now bad. A big issue I realized is that when you have a bad module in a pack, during a discharge test, all of the other modules are limited by the bad modules, So you don't really know for sure until you replace the weak ones, Then when you do, now the next weakest ones show up (that's my working theory) I used to think before that the good modules would have to work harder to make up the difference but now I think of it like a chain, only as good as it's weakest link. It would end up taking me three or four attempts until I finally was able To get the pack to stay within spec. After all of that, it would only last a short while, the longest it lasted was about 10 months. Perhaps the worst part was when the battery would fail, it would shut down the truck completely, leaving it dead in the water. When I open the pack I discovered that it had blown off the top of one of the replacement modules. Myself like others here, assumed that gen 2 Prius modules are the same, I don't have evidence to back it up but I believe that gen 3 Prius modules are different, they have slightly higher capacity and C rating and perhaps higher operating temperatures. I believe that these modules may have been used in the Toyota Camry hybrid and other larger Toyota hybrid's, excluding the Highlander and Lexus, I also believe that they were used in the GM 2 mode hybrid. The reason why I think that is because with The hundreds of Prius packs I have rebuilt over the years, I've never had one crack the case of a module, I've seen it three times, sometimes on the top and sometimes on the bottom, only on two mode hybrids. It does seem that the two mode is pretty tough on the battery, they definitely increased the power limits compared to Toyota, just like the Camry is harder on the battery than a prius. Now it's at the point where I won't even attempt to rebuild a two mode pack unless it was under 200 K because I've done it enough times, I had to redo it multiple times just to get it working on the bench, and then it fails a short while later, at least with the Prius it goes into limp mode but if you have a module crack then it shuts down the truck completely, that's a liability risk I'm not willing to take. I also think that the larger the pack, the more modules you have, The harder it is to keep voltage variance within spec. On a Prius with 28 modules it's pretty easy, once you get to a camry with 34 or a 2 mode with 40, It requires having modules that are extremely close in performance and capacity. I was thinking about how The Prius, this little car Has 28 modules, and a full size crew cab truck with a 6 L V8 has 40 nodules, just 12 more than a Prius, if my math is correct that's only 43% more battery capacity for a vehicle that weighs twice as much! If I were to apply my linear logic, double the weight, double the power demands, double the battery capacity. The issue is that they cannot put two of these modules together in parallel and then in series. If they could do that it would allow them to pull more current without damaging the modules. But of course they didn't do that, they only increased the capacity by 43% (instead of 100% increase), and I believe that's why these fail and are hard to rebuild. Probably the best option is to find a used pack with lower mileage, or to find a shop that will sell you 40 modules at a prorated price. That's what I do I buy brand new GEN two packs From the dealer, then I rebuild Prius, Camry, and two mode packs from those. At least then the customer doesn't have to buy two Prius packs upfront, but it's definitely not cheap. I am working on a project to design a replacement battery pack, using Lithium batteries, while still keeping the original battery control ECU, And just fooling it by manipulating data and getting it to do what we wanted to do. It would then be a plug-in hybrid which would be pretty awesome, but I'm nowhere close to finished. I think it is a good option for two mode, highlander and lexus but don't hold your breath lol. I made a new year's resolution that I wouldn't attempt to rebuild 2 mode packs anymore because it's usually a complete waste of time!

PS: If it was a voltage sensor lead issue, you should see higher resistance also

 

Another maneuver you guys should consider logging is the following.

From less then 50% SOC reported in Auto-Stop.

Reduce as many accessories as you can and accelerate from zero ever so slightly.

If you can see the near "real-time" HV battery power try and get it above 20 kW but not much more.

From a nearly steady load of over 20 kW hit the gas to about 35% not WOT quickly. This will force Auto-Start.

Take a look at maximum power used to propel the 3-Ton Sport Brutility and start engine.

More will be revealed if you do.

 

Welcome back.

Concerning your "power" calculations, you are incorrect. There are a different number of modules in various packs to permit operation at the same CURRENT. I've personally seen discharge currents of 150A and charge currents of 90A in a Gen2 Prius. I've noted the same in Camry, Gen3 Prius and multiple GS450h. All the modules care about is current, and that's why packs have different numbers of modules - to permit operation within the current limits. The systems are designed around those limitations. While weight is a factor, it's not a linear correlation.

Concerning "different" modules, you don't have evidence to back it up because there is no evidence to be had to support that conclusion. In 2009, Toyota changed the module design to provide a SLIGHTLY lower internal resistance. While that claim has been made, I have personally measured modules made in 2003/2004 with over 200K miles that operated in a mild climate that measures exactly like a BRAND NEW Gen3 module for a Gen3 vehicle. By brand new, I mean personally purchased brand new pack fresh from Toyota - never been in service.

Toyota Modules installed in all 2007-2009 hybrids all come from the same production lines. There is no difference of any kind beyond normal variation in manufacturing.

They are DEFINITELY not higher capacity. If anything, the newer modules tend to have notably lower capacity (5500-6000) than the modules made for the early years of the Gen2 Prius (6500-7000).

Side notes: the design change introduced in 2003 for the Gen2 modules produced substantially lower internal resistance than the Gen1 modules. This can be readily measured. Gen4 modules produced since 2016 are now being produced for all replacement packs and have no measurable difference.

The bulk of the changes to the NiMH module has NOT been to make a better battery. It's been to make a CHEAPER battery (for Toyota, who owns 80% of the company that makes the modules). For all intents and purposes, HEV NiMH technology peaked in 2003. Improvements since then have been negligible.

I have personally touched THREE Gen2 Prii that blew tops of their original batteries. I am aware of several more via second hand information directly obtained from other trusted service providers. Blown top modules are almost always caused by a cell failure. This is exacerbated by abuse - driving the vehicle with an intermittent battery problem or obviously week battery. The reason this is more common on the GM is because it's battery management is downright abusive, and it continues to abuse the battery well past the point where Toyota logic says the battery has failed.

Bottom cracking of modules is almost always caused by overcharging - typically by someone attempting to recondition a pack by charging at 1A for extended periods of time.

Every single discharge test posted of a suspect GM battery has shown PERVASIVE damage. Typically only 1-2 modules within a GM pack are even near 50% rated capacity with the remainder in the 10-20% range.

Most Gen3 or equivalent systems (Camry, Gen3 Prius, GS450h, GM, etc.) have poorly designed cooling systems compared to the Gen2 Prius. The suffer far more heat damage. They also tend to have user options for EV, power and "ECO" modes - all of which tend to increase strain on the battery.

Your approach with new packs is the best option.

Your conclusion on 2 mode battery rebuilds is spot on unless you're using the Gen2 new pack method.

Lastly, do your homework on Lithium:

1. There have been MULTIPLE companies that produced very workable PHEV conversions for the Gen2 Prius. They are ALL out of business now.
2. Only the best and most expensive Lithium can handle the CHARGE currents NiMH shrugs off as a tickle. You have to size your Lithium back for the CHARGE current. A lithium pack typically has substantially more capacity simply for that reason.
3. LiPo is flammable and explosive. NiMH won't burn unless sustained with a torch - you might get a little smolder once the torch is removed.
4. Best is to do it solely for yourself for fun. Commercially, it will fail.

 

Wow some great suggestions and info thank you hillbilly and keith! Yes the power demands are quite high on these trucks, I'm very impressed that these batteries last as long as they do with no active BMS! Mr. Keith, thank you for clearing up my misunderstanding, it seems I started thinking too hard because what I thought before was they increased the number of modules, to increase voltage (and power) while keeping current limits the same; then somebody started talking about thicker plates, different modules with higher C rating, I started chasing that scent, but thats wrong. In regards to Gen 3 modules, dangit your right, I was very disappointed when I bought 5 Gen 3 packs from a local junkyard and only 1 of them was good, 1 was rebuildable, and the other 3 were unusable in this application (they make great trolling motor batteries though lol). I can confirm they were overheated, measuring OCV, starting from the end and moving towards the middle, the resting voltage drops and then goes back up towards the other end. During discharge the deviation is rapid and large, they were clogged up with dust and junk, not very surprising. The ones that worked, yes the capacity was about the same, if not lower, than most gen 2 packs, so I agree with your assessment that they cheapened up on Gen 3, didn't make them better. Actually I was joking with a friend that with Gen 1 there's always issues, with Gen 2 they fix those issues, by Gen 3 the bean counters have cheapened up the car and now it has issues again (Gen 3 Prius egr cooler/ head gasket much?) Gen 4 i'm not totally sure yet lol.

In regards to bottom cracking and overcharging, i'll take your word for it. It's probably worth mentioning that the DC power supply I used to use for charging and balancing, can do about 300mA max, definitely cannot do 1A, even if I thought it could (good thing it couldn't lol come a long way since then ).

I have done a little homework on the lithium, and yes the only way to make it work, safely(ish), is by significantly increasing the pack capacity and paralleling multiple cells together to handle the amperage. I agree with your point about the difficulty of turning a prototype into a commercial product; doing something like that would require developing an entirely new business model based around refurbishing hybrids and leasing them with all costs included, probably as a nonprofit charity research organization, convincing a Chinese lithium battery manufacturer to sell cells at 1/3 the price until the venture becomes profitable, applying for grants, getting help from the city's economic development director, angel investors, help from the OEM's, insurance underwriter sponsors, collaboration with a university, convincing lawmakers and the public that rebuilding hybrids and perhaps upgrading some of them into PHEV (that need battery replacement) and leasing them to people that typically couldn't afford an HEV, is the best way to get more HEV onto the roads (in addition to making new ones) Man that's a tall order, hope somebody's working on that .... ok ok it's me that's what i'm trying to do with EVA Electric Vehicles for All (sorry for the promo but I can't help myself)

A question about new OEM gen 2 packs, I assumed what Toyota is selling is whatever they're currently using in production; do you think they are actually gen 2 modules? Like NOS or actually new but different modules than current ones?

What are you doing with Highlander and Lexus hybrids that use the larger modules? The price on those is ridiculous, I wish I could give those customers some options but at this point there's not much I can do.

Thanks again for this thread because it matches up with exactly what I've been seeing, glad to know i'm not alone in that regard

 

I completely agree with your summary of the progression from Gen 1, 2 and 3: 1) New tech way better than previous but with some unforeseen issues; 2) Fixed issues and made a solid product until "value" engineering took over to make them cheaper.Introduced some issues with tendencies for leaking from 07-09, but still way better than Gen1; 3) Toyota: "holy crap these Gen2 batteries are solid. We can push them a little harder and screw up their cooling system."

Gen4 is hopefully... no worse than Gen3. I like to think on the Gen2 with their top-down cooling flow, the smooth tops might help cooling a tad.

(1) Not sure, but Toyota was using Gen2/3 style casings up until somewhat recently for all Gen2 and 3 new packs. I would assume that they're going through years worth of raw material inventory and/or were tooling up to increase volume on the Gen4 style. The last 5 Gen2 packs I've purchased are all the Gen4 style with the smooth tops. They were actually made back in May/2019. I've purchased Gen2 packs with Gen2/3 style tops that were made much more recently than that. I can only conclude that were running both lines parallel until they could come online with the single type. It is also possible that they are just filling orders with whatever inventory they have. Note that I believe that all modules have the same internals: separators, plates, interconnects, etc. If that weren't the case, I would detect it on some of the precision measurements I take.

(2) I generally don't. On two occasions, I've sourced a salvage units and fully tested/reconditioned all modules to > 5Ah of capacity. I've received maybe 8 calls on Highlanders in 4 years. I still offer that as a solution, but few want to wait the 1-2 weeks that can take unless they REALLY want to save some money.

 

My friend was saying that the top down air flow is a better way to cool, which confused me at first, again with "linear logic" heat rises, so why would you want to work against it? Perhaps slightly higher pressure, better cooling?

I just started getting a few calls with Highlanders within the last year; Lexus is picking up too. I was told that the highlander pack is a major pita to rebuild; just getting it out takes more work than prius. I think the achilles heel of gen 3 prius/ camry, highlander and lexus, is the egr cooler. It gets clogged, the water pump or thermostat (or both) fail and the head gasket blows. It's hard to believe with a vehicle so smart it cannot shut down before completely overheating, but I've seen them miss some pretty serious problems and saying everything is fine. How much does it cost to have the egr cooler cleaned, replace the head gasket, machine cylinder head, water pump/ thermostat replaced, HV battery charged/balanced (ran down to 4%), intake/fuel system cleaning, engine coolant system flush, oil change? At my shop it came out to $2,350 , quote from my local dealer was north of $6,000! Who's going to shell out that much cash for a 2010 prius with 225k mi ? Probably not many people. All of these vehicles will have to deal with this issue or they will be scrapped; which makes me very sad. I think in the next 3 years the market will be flooded with all these hybrids that nobody wants/knows how to do anything with. Since the resale value is low and the repair costs are high (somewhat artificially), we will see many of these vehicles "financially totaled" . I'm trying to change that, I think we shouldn't let any good HEV go to waste, get the most out of them that we can and then switch to second life usage. Basically i'm trying to make the passenger vehicle market more closely match the commercial vehicle market. You don't see companies auctioning off their semi trucks and jetliners every 3 years because they're expensive, they were built to last and be fixed. Also, there's only a handful of models to choose from because everything must be standardized for safety and logistics. If we started doing the same with passenger vehicles, it would stop a lot of this waste, while also helping people, and the environment!

 

It's not that top down air flow is a better way to cool, look at the Camry - it's top down. It still sucks. GS450h, HS250h - top to bottom. They all suck.

Gen1 is bottom to top, and while it has its own problems, the cooling system isn't particularly bad

The flaw is the inlet. Look at the Gen3 Prius - fan is 6" away and undergoes expansion as it enters. Problem is the expansion nozzle is too short, and the airflow is dirty as hell. Camry is the same way except it's worse. It makes a short distance expansion followed by a 180° bend.

The Gen1 inlet isn't great, but the "suction" design helps clean up the airflow. The Gen2 undergoes a relatively gentle expansion over a much longer distance resulting in more uniform inlet flow. Basically, then entire opening is flowing a reasonably uniform amount of air. There's still a bias towards better cooling at the ends due to proximity of the inlet and stagnation pressure at the far end, but you get a reasonably uniform plenum that helps drive air down through all passages.

Imagine the Gen3 having no expansion. You get a "jet" of flow roughly the size of the fan outlet. There's a centralized column of air. It disrupts the stability of the lower plenum and produces non-uniform flow up the channels.

Highlander pack is big and unwieldy, and the 8 cell modules are riveted in place. They have to be drilled out and replaced with pop rivets. There are 2 identical outer groups of modules and one central one. Swapping module groups is a piece of cake and is probalby the best way to start. There generally isn't a lot of deterioration in their capacity due to the 3 cooling fans and the improved thermal conductivity of the module cases (metal instead of plastic). They tend to drop cells like the Gen2 rather than the widespread damage/deterioration of the generation 3 hybrids.

"Financially totaled" is silliness incarnate. Cars are depreciating assets, and people rarely factor in REPLACEMENT costs when considering "fix or buy new". Here's how I look at it: If I buy a car for $10K, and I get 100K miles out of it, I'm a happy camper. That breaks down to $0.10/mile. If a car is generally reliable (it's not breaking down several times a year), and I can reasonably expect that I'll get 10,000 miles for every $1K spent, it's a no brainer. It's the known, it's the car that has already demonstrated reliability, and it doesn't have a hefty price tag and likely increased insurance associated with it.

IMHO, total cost of ownership is the only thing that matters. Go buy a new car, and the 20% hit you take on depreciation in the first year is almost always much more than the cost of the repair you were considering on that old car that's "not even worth the cost of the repair."

IMHO as well, the idea that "this car isn't even worth the cost of the repair" was embedded and is perpetuated by the dealerships to encourage car sales, NOT because it makes the most financial sense. Replacing a car is RARELY the correct choice financially unless it's overall poor reliability is burdensome (breaking down several times a year).

 

Ok that makes sense about the airflow, having a uniform plenum is definitely important and I can visualize what your talking about, and I can see it with Camry and gen 3 packs.

Yes my friend was telling me the Highlander pack was not made to be rebuilt, not that any other Toyota hybrid packs were ever intended to be rebuilt, but they at least made it relatively easy. It's cars like the Highlander, Lexus and 2 mode hybrid where I wish I had a lithium drop in pack replacement. Realistically the price tag would end up around $10k after battery, charger, bms, and everything else.

"Financially totaled" is nonsense. I talk about this in some of my articles and videos. Most people think it's planned obsolescence by the OEM but I think you hit the nail on the head; the problem is the dealership model. It's way too bloated, too much pork, think about how much of the customer's money goes towards paying for that huge, shiny dealership facility, the staff, and of course, the typical multi-dealer multi-millionaire owner that expects a big slice of the pie. Then factor in financing companies, full-coverage auto insurance, and fees; now somebody that is paying $500/month to lease the car, $200 goes to the car payment, $150 goes to financing, and $150 goes to collision insurance.

The market value of the car always comes up when talking about battery replacement. The reason everybody wants the cheapest fix possible is because they don't want to pour more money into a car with a low resale value. But there's other types of value; carbon reduction value, waste/pollution reduction value, resource/energy conservation value, utilitarian value. It drove me crazy before because I know the best solution is a new battery but hardly anybody goes for it, even with me trying to bring the price as low as possible. I knew a working Prius is priceless to a lot of people, so that's why I started researching this stuff and eventually started EVA.

You are 100% correct, the total cost of ownership is the main thing to look at. A new car can lose 2/3 of it's value in the first 3 years; HEV can lose 72.7% in those first 3 years. If you read the EV market forecast newsletters, they're all saying strong hybrids no longer make sense; either get a BEV or get a 48v mild hybrid, nothing in between. I strongly disagree with this assessment for a number of reasons. Perhaps my biggest point of disagreement, is where they compare 3 sedans of a similar price, a normal ICE, a HEV, and a BEV. The lifetime is defined as 10 years 160k miles. No surprises that only measuring during that period, the numbers turn out most favorably for the BEV. But, if we doubled the life to 320K miles, what would it look like? Well I say BEV have a DEFERRED cost of ownership; not many big problems until around 200k and then you may have to replace the battery pack. If a 1.2KW Prius pack cost $1,650 wholesale, how much does a 80KW Tesla pack cost? Also, the main thing they use to back up their case, is the total cost of ownership. Now, they're using the average cost of servicing these vehicles; at the dealership. And having a hybrid serviced at the dealership, is artificially expensive, so the combination of the deferred cost of ownership for a BEV and the artificially high service cost of an HEV, skews the results in favor of the BEV. I don't think this is necessarily nefarious, they're just going off the data they have at hand, which is incomplete, doesn't capture the true scope of the market.

Now, lawmakers are using these reports and experts to help craft sustainable transportation policy. The way the laws have been written, it heavily favors BEVs, while discouraging the production of HEV and PHEV. That's why so many automakers are saying they're 100% on BEVs now, not even trying with HEV, they can make a bunch of gas guzzlers, plus 1 or 2 BEVs, and their fleet average is acceptable.

My plan is a bit different. We can only build a certain number of BEVs per year because the number of lithium batteries is limited. Which means, Perhaps we can get 5% of the vehicles on the road to be BEVs by 2025 with that amount of batteries. Or, what if we could get 15% of the vehicles on the road to be HEV or PHEV by 2025? What makes a bigger difference in emissions and waste? What if the HEV we built today were designed with the intent of upgrading the battery when the original is exhausted? We could create many more HEV today than we can BEV; and then in 5-10 years we will maybe have solid state batteries or at least enough lithium batteries being produced, that we could upgrade those HEV into PHEV. Something that's super important is the loss rate of HEV. If we are trying to get 5% of the vehicles on the road to be HEV by 2025, theres a couple factors to consider. 5% of vehicles on the road in 2025 is substantially larger than 5% of vehicles on the road now in 2020; so not only do you need to make more of them, for cheaper, but also faster to keep up with this growth. Then, it's all about the loss rate. Let's say we were increasing the number of HEV by 20% per year, but we were losing 15% per year; so we are only increasing it by 5% per year. If we reduced that loss rate, kept these cars on the road all the way to 320K, we could effectively double the number of HEV on the road. It gets better, because fixing a Prius at 160K, it's already repaid it's carbon debt (for manufacturing/transportation) many times over; the only resources going into it at that point is labor and whatever is needed to fix it (if a used/refurbished part is used, that's even better, economically/ environmentally speaking).

I'm trying to get support and funding, to help small businesses like ours that work on these vehicles; because we don't have lobbyists and lawyers to do all that for us. I realized though that what we are doing is super important work, I could make a convincing argument that rebuilding HEV is just as important as building new HEV and BEV. I mean, shouldn't the transition to sustainable transportation, itself, be sustainable? Maybe it's ok to get a new iphone every year, but a BEV like a Tesla, is equivalent to literally thousands of iphones, just think of a pickup truck bed full of iphones and there you go, that's basically the amount of materials required to build a Tesla. And if HEV and BEV can really do 500k+ miles, well why the hell aren't we doing everything we can to ensure that really happens with most of these vehicles? The Nissan Leaf drives me crazy because the care itself is actually pretty good; the problem of course was the lack of a battery thermal management system. So now Nissan brags about powering stadiums with old Leaf batteries, my question is, what'd you do with the rest of the car? Scrapped it of course! Most of those Leafs had under 100k miles; I'd be curious to know how many of them actually made it to 160k. Here's my analogy: You got these flashlights with rechargeable batteries, your flashlight starts dimming a bit and not working very well, so you take out the exhausted rechargeable batteries, put them to the side and save them, then you throw away your perfectly good flashlight, and go buy a new flashlight with new batteries and pat yourself on the back for being so environmentally woke

Ok final thought, about lifetime carbon footprints. Who do you think has a higher lifetime carbon footprint? A. Somebody that lives in LA, solar panels on the roof, drives a Tesla, jetsets around the world, pays to have trees planted and shops at whole foods. or B. A hillbilly prepper dude in Appalachia that drives a 1990 F150 (they fix themselves, with used parts), hunts and grows there own food, gets power and water from micro-hydro.

My research so far indicates Mr. Hillbilly is much more of an environmentalist than LA dude. I love BEV and HEV, and they are important, but I've realized that sustainability is about so much more; and the more high tech you try to make sustainability, the tighter the margins.

Ok I think that was a long enough rant; thank you!