Li-ion battery health measurements by reading the Battery Pack Capacity signal

Interesting read-out. You've made three assumptions not listed; 1) that the battery pack capacity is independent of temperature and 2) that the measurement is reliable within 2% and 3) that time is the other axis instead of miles. If any is important (and I suspect they are), then your Clarity battery capacity may be higher or lower than you think, compared to OEM. So, a one-time measurement at 82F ambient may not be enough for creating any lines/curves on graph anyway I also don't think you can do inter-car comparisons, giving the driver variable. Bottom line: get your long-suffering dealer to check your Clarity's battery every year at 82F ambient and report back in 5 years with 5 points on your line of Ah vs miles. (Tongue in cheek of course ).

In reality, if enough folks get a battery pack capacity measurement and report back, it would be interesting collective data.

 

I have read a great deal on the degradation of the Tesla batteries and the capacity charts almost always show that there is an initial drop off of a few percent, which then starts to flatten into a much more gradual decline.

I suspect that this is probably true of the batteries used in the Clarity. There will be an initial drop down to 95% or 96% capacity (which is not going to show on the gauge because Honda is not stupid enough to let the gauge really show 100% capacity because the batteries are not really allowed to charge to 100% capacity) but after this initial drop, the capacity will stay in the high 90s for a few years.

The chart on this page shows how it goes with the Tesla, and I would expect the same for the Clarity. Initial drop will be quick and sharp, but only a tiny percentage of capacity, then the slope flattens and stretches out.

https://www.greencarreports.com/news/1110149_tesla-model-s-battery-life-what-the-data-show-so-far

 

I have been worried about a decline in my battery capacity within my first 8-9 months of ownership. I've been noticing a steady decline in range along my daily commute. I live in Southern CA so weather isn't a big factor.


I brought my car in for testing and my battery capacity is at 51.8Ah and my V1 voltage is 302V. That's a 6% decrease in Ah according to the figures in the original post here and 8% in kWh assuming a starting 17 kWh as stated by Honda. However my average driving range on battery has decreased by about 11% from the first 3 months of having the car to now. To me these figures are disturbing, but Honda said everything looks normal. I am planning on call them to ask what they consider "normal". I'm pretty annoyed, this seems like too much of a decline too fast.

 

Screenshot provided by my dealer does not show the V1 voltage; Software Title bar says version 1.004.0064 and first two listings are 'Absolute Throttle Position Sensor' and 'Air Temperature Inside the Vehicle'. The screen indicates there are additional values farther down, so maybe in this software version the V1 voltage is on the second page. Reposting from another thread: As of 19 Apr 2019, Battery capacity measured 52.9Ah. Measurement at PDI not provided (probably not done). Current mileage was 18.5k. Rough guestimate of 12k on pure EV mode.

Assuming the battery capacity was at 55 Ah in Dec 2017 and knowing it is currently at 52.9 Ah, a linear projection would be that it would fall to the warranty replacement level (36.6 Ah) at the end of year 2029.

I don't baby this one nearly as well as @KentuckyKen does his. Most of my accelerations are normal and not as though I'm trying to hypermile; decelerations are more planned.

 

Reposting from another thread:

After 13 months and 19k miles I am at 54.0ah. I’m really pleased considering the huge weather swings in Kansas City. We go from 100 degree highs for the month of August to 0 degree lows during February. For the record I took delivery of my car as soon it arrived from off the boat from Japan so I am sure that helped.


Sent from my iPhone using Inside EVs

 

KentuckyKen, what is the PDI and where did you find that information? I have tried contacting the dealer and Honda directly about what is considered normal degradation and can not get a straight answer from them. I'm wondering too about what happens if it is on track to reach 36.6Ah quickly but isn't there yet - will they really not replace until it gets to that point?

 

It's too bad the Battery Pack Capacity signal cannot be read with an OBDII scanner. Because it takes a dealer's service department some time to perform the Battery Pack Capacity check, it would be awkward to be taking your Clarity in week-after-week to get the latest reading as you track the slow decline. If the Clarity PHEVs going to California (10-year warranty) are the same as the ones going to the other North American locations (8-year warranty), then it's likely Honda engineered the battery pack to last at least 10 years. Unlike the air-cooled battery pack in the Nissan Leaf, which has been known to deteriorate rapidly, the Clarity PHEV has a liquid-cooled (and, in Canada, warmed) battery pack, so it is much better protected from battery-killing heat.

 

I think the consensus is the the battery pack is the Blue Energy EHW5 or EHW5B model used in the Accord Hybrid and the Clarity Fuel Cell. See this Accord Hybrid teardown and the product info page with a list of Honda vehicles which use the pack.

 

It's not linear -- at least not over the relatively short period you're talking about -- and it's much more closely linked to total distance than time.

Below is a graph of actual third-party reported battery capacity degradation data for the Tesla Model S. The graph shows that over the first ~30,000 miles of travel, the capacity loss is relatively steep at first, but rapidly flattens out over the course of that distance.

Caveat: Please note the scale at the left. The graph is distorted to exaggerate loss over time by cutting off the bottom 82% of the graph! An overwhelming majority of the data points show less than 10% degradation over ~300,000 kilometers (~186,000 miles), and the worst is ~16% loss.

Of course we can't expect every BEV to follow this same exact pattern, because different BEVs use different cell chemistries, and different battery packs handle their cells differently. But I would expect to see a similar flattening over time for capacity loss in other BEVs, since we see the same flattening of capacity loss, for long-term repeated cycling, in li-ion batteries in general. (The Leaf may be an exception for that; the amount of fade over distance varies a surprising amount from car to car. Lack of consistency in capacity loss is a big problem with the Leaf.)

 

The marklines.com automotive industry site (which has more current info than the Blue Energy web site) states that Blue Energy supplies the Clarity Fuel Cell, Electric and PHEV. (sign up for a free trial to follow this link, or google "clarity phev 27.3 Ah" to see the text from marklines.com in the search result)

The same site indicates that the PHEV is not due to a redesign until 2023.

 

What automaker has been using the Blue Energy cells the longest on what cars?

 

I wouldn't assume the Honda Clarity PHEV's battery pack will degrade, on average, only ~8% over the same period. A PHEV's pack is much smaller than a Model S85's (BEV) pack, so it gets cycled a lot more frequently. I think it's safe to say that the Clarity PHEV will likely experience, on average, significantly more battery capacity degradation than a Tesla car does.

But on the plus side, it's quite likely that Honda chose a battery chemistry that holds up better to repeated cycling over the long term. Tesla chose cells optimized for high energy content and to some extent high power; a PHEV manufacturer with competent engineering will choose cells optimized to stand up better to repeated cycling. I think Honda has shown it's quite competent in this area, despite some "angry bees" concerns.

KentuckyKen, my purpose in posting that Model S graph was to show that for li-ion batteries, the degradation is far steeper at first than it is later on; that you shouldn't extrapolate the capacity loss over the first several thousand miles, or even the first several tens of thousands of miles, to an expected 10- or 15-year lifespan of the car.

 

It has been established that temperature has an effect on li-ion battery capacity. With higher temperature, capacity actually goes up; that's one of the reasons why it's so hard to accurately measure li-ion battery capacity.

But I have no idea how much that effects capacity. It would be better to test it at room temperature (72° F), but I have no idea how much difference there is at 82° F. Perhaps the difference is insignificant; perhaps it's not.

​

 

Neil...look in the canvas folio that you got containing the owner's guide and other stuff when you took delivery. The (presumably) filled-out PDI booklet should be in there.

 

It is true that a PHEV battery gets cycled more than a long range BEV battery, but on the other hand it is designed to maintain more capacity in charge/discharge cycle. Clarity gets full charge in about 12.5-13 hours on Level 1 at 11 amps. That is about 12.5/13 kWh, considering charging efficiency. So about 72% of the battery is used in each cycle. That is a lot less that what Tesla uses. With time probably they keep increasing this ratio, so a 15 year old battery could use for example 90% of the remaining capacity. I don't expect significant range drop in a typical life cycle of 10 years or so.