Battery Capacity Loss Indication?

[miimura]

When a RAV4 EV is driven enough miles and ages through the years, it will gradually lose traction battery capacity. This is an eventuality. The question is, how will the car indicate this capacity loss?

We know the range indicator (Guess-O-Meter) next to the fuel gauge is based on your past driving efficiency, so this is clearly useless for actual battery capacity indication. The Leaf has capacity bars on the gauges and it is now well known how much capacity each bar represents. The RAV4 EV State-of-Charge indicator is 16 bars that roughly represent 2kWh each. If the battery were to lose 2kWh capacity, would the 16th bar not come on after a full Standard Charge? What if you use the Extended Charge? The reason that I'm asking is that the car already doesn't have any indication for the capacity above the Standard Charge level. If the car did not have any indication of capacity loss until the total capacity dropped to 15 bars worth of energy, it would be possible to have lost 28% of the capacity with no indication to the owner/driver. (41.8-(15*2))/41.8 = 0.2823

While I think the Leaf capacity issue was made worse by the clear indication of traction battery capacity loss, at least from a PR perspective, the scenario above is far worse for owners.

 

[TonyWilliams]

Just like there is no indication for a 100% charge over an 80% charge, there surely won't be any indication of degradation!!!

If the battery is degraded 50%, it will show all 16 fuel bars for an 80% or 100% charge, just as it does now. That is the same as the LEAF, by the way (except the LEAF is smart enough to show 10 of 12 fuel bars for 80% charge and and all 12 for 100%)

What's different in a LEAF is that it has an actual degradation meter, and Rav4 does not. Of course, that degradation meter in the LEAF won't show any loss of capacity until the battery is well past 15% degraded, then each subsequent capacity segment is 6.25% loss according to the LEAF service manual.

When the Rav4 degrades, it just won't go as far!! Obviously, there is data in the various CAN buses that need to be decoded, just as they have been for the LEAF.

 

[Dsinned]

Wouldn't you have some idea of the degradation by how long it takes for the battery to fully recharge? This too may be ineffective, because of how cell balancing works on the RAV4 EV. However, if you have a power line monitor on your L2 EVSE charging station, you have a way to determine the duration of each recharge, but you would have to start from the same initial SoC each time, which at best is only an estimate because of how the GoM works.

Bottom line, I don't think there really is any practical way to keep track of battery degradation in the RAV4 EV.

 

[TonyWilliams]

Bottom line, I don't think there really is any practical way to keep track of battery degradation in the RAV4 EV.

Absolutely there is. A controlled driving test will do just that. See this thread to see how I did that for 13 total Nissan LEAFs in Arizona.

 

[TonyWilliams]

Bottom line, I don't think there really is any practical way to keep track of battery degradation in the RAV4 EV.

Absolutely there is. A controlled driving test will do just that. See this thread to see how I did that for 13 total Nissan LEAFs in Arizona.

Also, as you suggest, I recommend a "verification of data" test. Refuel the vehicle at the same battery temperature and rate from the "control" charge. On the Rav4 EV Gen II, I pumped fifty and one half kWh from a "Turtle" mode car to 100% at 30 amps at roughly 70F.

Obviously, ambient temperature plays a REALLY big variation in this, as the battery TMS will consume more energy when cold or hot while charging. Therefore, I recommend as close to 70F ambient temperatures as possible as a control. This was a consideration also in the LEAF, but not because of TMS consumption; it's because a cold battery is more inefficient to charge than a hot one. Also, a cold battery stores less energy than a hot one.

When you're done with a careful range test to turtle, and a complete "fill up", the two adjusted data points should somewhat closely indicate how much capacity the battery has lost.

 

[Dsinned]

Tony, as I said, there is NO PRACTICAL WAY to determine battery degradation in a RAV4 EV.

The scientific method you describe is maybe one way to substantiate the grounds for filing a class action law suit against a major auto manufacturer. This seems a bit extreme to me. However, the "average" owner would never be so inclined to do the same. And fortunately, the vast majority of RAV4 EVs sold thus far, are not located in Arizona. :mrgreen: