Good/Bad/Ugly Batt Kapa Max readings?

My 2017 i3 is supposed to arrive this week. When it gets to CarMax, I plan to look up the Batt Kapa Max. I've learned how to do that, but what I don't know is how to interpret the value that I find. This car has 11K miles on it. What should I consider a good reading, a bad reading and a 'run away fast' reading?

Thanks in advance. I'm getting very excited to get this car!

Kimberly

I don't recall ever reading of a low Batt. Kapa. max value for a 94 Ah battery pack. To me, this seems to be a problem only with some (many?) 60 Ah battery packs.

The nominal new 94 Ah usable battery pack capacity is 27.2 kWh. Compare that with the Batt. Kapa. max value for a rough estimate of the degradation of the battery pack.

If you want a point of comparison, I have a 2017 REx with the 94 Ah battery pack. I'm the second owner, but my car originally entered service in Sept. of 2017 and currently has 19,000 miles on the odometer. I've looked at the value of Batt. Kapa. max several times since I purchased the car this past March. It has varied slightly in a tight range between 29.4 and 29.6, or about 108% of its rated capacity of 27.2 kWh.

Although the "rated" capacity of the battery is 27.2 kWh, I believe that number is a bit of an under-rating that BMW uses to reduce the number of battery packs that it has to replace under warranty, with the true usable capacity of the 94 Ah battery around 30 kWh when brand new. (This is a bit of guesswork, though.)

Of course, my car is just a sample of one. It could have an extraordinarily good battery, but it's more likely just an average battery. Given that the car that you are looking at has fewer miles than mine and is roughly the same age, I would expect a value around what I see. My car is currently living through its third Texas summer (previous owner also lived here) so the battery cooling system and BMS does seem to work very well, at least for the 94 Ah batteries.

That's a great point of comparison. And I live in Middle Tennessee, and the car is coming from Georgia, so it has probably seen a few hot summers as well. Thank you!

FWIW, TX is huge, and the weather can vary a lot from one place to another through the seasons.

Generally, the i3's battery cooling capability is decent. It gets taxed more when using a DC fast charge than the more common EVSE (max 7.4Kw on an EVSE, 50Kw on a CCS charge). Unlike most all versions of the Leaf, where it relies on passive, air cooling, the i3's liquid cooling is a lot more robust (and costs more!).

jadnashuanh said:

FWIW, TX is huge, and the weather can vary a lot from one place to another through the seasons.

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That's a good point. My car has happened to be in Austin for its entire life, with brutal summers and mild winters. So my car has seen a lot of heat and not not much cold.

Generally, the i3's battery cooling capability is decent. It gets taxed more when using a DC fast charge than the more common EVSE (max 7.4Kw on an EVSE, 50Kw on a CCS charge). Unlike most all versions of the Leaf, where it relies on passive, air cooling, the i3's liquid cooling is a lot more robust (and costs more!).

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Again, good point. No idea how the original owner charged the car, but I rarely use a DCFC. I almost always charge it on a 240-volt public EVSE that delivers about 6.1 kW of juice.

FWIW, many commercial EVSEs are fed with 208-v nominal power. 208v*30A=6240w. 30A is a fairly typical max current on them as well, although newer ones may be 32A.

Depending on how hard the vehicle is run, how long the trip is, and whether they set a departure time, would all play a part in how hot the battery pack got. Once it's hot, it can take a long time to cool off. Higher demand means a hotter battery. So a high speed run done without setting a departure time, then sitting in a hot parking lot and trying to charge, especially with a CCS unit, could be the worst of possible conditions and affect the battery longevity probably the highest.

Batteries are often rated at how many charge cycles they can support and, given the same range, a smaller battery pack will need more recharge cycles than a larger one, and that can play a factor in it as well. A charge cycle is defined by a 0-100%, so one of those is approximately equivalent to 10 recharges from 90-100%.