Budget Battery Capacity Readout

2018 Honda Clarity (Canadian Touring version) ~134,000 km
- nearly all in EV mode
- very infrequent charging (usually level 2, short stints of 30 min or so)

Bought the V gate OBD2
Car scanner app (pro)

Installed all of Mr.Fixit's PIDs

Drum roll please....

Battery Capacity reading - 54.98

Wow! Really? So if I ever stop using my Clarity like a straight up ICE regular hybrid (when I get charging and don't need to drive 200km daily, in one go), I will still have most /all of my battery still?

That's amazing, and totally helps me decide to buy out my lease in. 11 months time!

 

I second MrFixit's request that the three of you check this measurement on a monthly basis, and update us with your data. Given our small sample size, having three apparent outliers regarding battery capacity is very interesting, and worth exploring further.

 

There were some conflicting statements in the post. However, it was never stated at what SOC the battery has been kept.

 

vgate iCar Pro with Car Scanner:
2018 Clarity Touring
56,595 miles
Avg EV range is 33
Lvl 1 charge daily
Battery capacity: 44.5

 

This is what was stated.

I’ve driven 700 miles in one day on 3 occasions, and only lost 2-3 bars of battery capacity. Very infrequent charging” is vague. The SOC could have been kept at any percentage. And keeping it at 10-15% SOC isn’t ideal. I’ll go out in a limb and say the reading isn’t accurate.

 

No argument. Just going by what was said. I agree that the described driving habits and patterns indicate primarily HV mode driving.

I would say that based in my 700 mile trips, it would seem possible to drive 2000-3000 miles, in HV without charging, and still have a battery at ~50% SOC. An occasional bit of L2 charging could bring the battery to 75-80%. It is also entirely possible that the owner drove around most of the time with depleted batteries. I just wouldn’t make such an assumption.

 

How about this for a theory: The battery capacity only updates after a full charge to 100% where the cell leveling occurs, and that info is used to re-calculate battery capacity.

 

I think bringing the Clarity HV battery to 100% (actually about 90% of the absolutely full SOC given how the Clarity BMS works) may not be enough to reset the Battery Capacity value. For many Li-ion systems (especially laptops), the BMS requires a full charge from near 0% (about 10% of an absolutely depleted SOC for the Clarity BMS) to reset the battery capacity value.

Of course, this can be tested for the Clarity by taking a Battery Capacity measurement, along with the starting and ending SOC, for a series of charges. For these purposes, it would be nice if the HondaLink app would give the Battery Capacity along with the SOC. This would make such a study much easier to do.

LeoP

 

That’s definitely a theory. If true, it would imply that the battery capacity reading for any battery not recently fully charged would not be accurate. If we apply that to owners who diligently keep their battery between, say, 30-80% SOC, they would never get an accurate reading.

I’ll propose a theory from an alternative universe. Sensors measure current over time (Ah) and compare that to a percentage increase in SOC over the same time period, to calculate an Ah rating for the battery. Of course, charging from 0-100 isn’t completely linear, but the software should be able to compare a charge from 40-60% on a new battery, with a charge from 40-60% on a seasoned battery. Just a theory.

 

The graph of SOC vs. li-ion cell voltage is fairly flat (near zero slope) between 80% and 20% SOC. This makes for a great deal of uncertainty in determining SOC from cell. The BMS usually gives out SOC from knowing the battery capacity and then coulomb counting to know the SOC (from a starting point of a full charge event). To get the battery capacity, the BMS must be fairly certain of the SOC so a charge event from and to points on the SOC vs. cell voltage plot where the SOC has less error is needed. Thus, a charge event from above 90% SOC to below 10% SOC is usually needed for the BMS to reset the battery capacity value.

LeoP

 

2018 with 35k miles. 70 mile daily commute (with the exception of weekends.) Nightly charge on a 16a level 2 charger. I don't charge on w/e's because I don't need to. I should add that I don't baby this thing. I average 76 mph on the freeway and I live in Hilly San Diego. I MIGHT get 36 miles on a charge.
47.34.

 

We’re measuring mV’s. While 3.9V to 3.6V doesn’t sound like much, there are 3000 incremental measurements available that can be used to correspond to a SOC percentage between 80% and 20%.

Am I missing something here?

 

First, there is just 300 mV difference from 3.9V to 3.6V. Second, the chart shows cell voltage while being discharged at various discharge rates. At zero discharge, there is nominally about 100mV between 80% and 20% SOC for a typical li-ion cell. Finally, there is an error in measuring an individual cell voltage (and on measuring the pack voltage). The precision of the measurement (say 1mV) is usually less than the accuracy (less accurate than 1mV). It is not that accurate to determine the SOC from voltage measurements over only parts of the 80% to 20% SOC range.

And, of course again, we can look at the change in battery capacity over time as the Clarity battery is charged many times if we collect data (starting SOC, ending SOC, kW of charging energy, and the battery capacity before and after the charging event) for each charging event. I actually record all the data except the battery capacity for each charging event for our Clarity. I doubt I will hook up the AP200 or Elm327 for each charging event. That is why I lamented the fact that HondaLink does not provide the battery capacity.

LeoP

 

Copy that. I’ll just check in again at a Honda dealer in a few years and see how the battery is holding up.