Capacity Calculation

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Zeppelin

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Joined
Aug 9, 2021
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I have a 2015 i3 REX with 42,000 miles. My range has dropped to about 52 miles, so. I went through the process to get the car to do a self diagnostic test using the hidden menu on the dash. The result was Max Capacity of 14.6Kwh. If that is divided by the 22Kwh capacity when new, the result is 66.4% which would trigger a warranty replacement.

My question: is the 22Kwh used in the calculation or is the 18.8 usable capacity used in the calculation which puts me at 77.7% ?

I searched the forum and didn't see that this question had been asked before.

Thanks
 
All calculations for this that I have seen posted, use 18.8Kwh, as this is 'useable' capacity.

That said, not sure how much I would trust a single battery kappa reading. It can be as fluid and changeable as the range guessometer .

After a month or more of daily short trips (15 miles), with no preconditioning set or used, recharging daily or every two days, was seeing a decrease in range to about 55 - 58 miles on average, temps in the mid 90s F, Comfort mode, AC on, battery kappa reading - 14.3 kWh.

That weekend, did a long trip, taking the battery down to 6 miles left in range, set precondition and recharged overnight, range next morning was 69 miles - only 3 miles off 'new' advertised range of 72 miles, with a battery kappa reading of 15.
 
Zeppelin said:
My question: is the 22Kwh used in the calculation or is the 18.8 usable capacity used in the calculation which puts me at 77.7% ?

I agree with MKH that 18.8 is the number to use. BUT-- I also think it's worth noting that no matter what number you use, the only test that actually matters is the one BMW does... and they're extremely secretive about what that actually entails so we're just left reading Batta Kappa Max and whatever other tea leaves we can come up with!

Also, 52 miles on 14.6 kWh comes out to about 3.5 mi/kWh which is not impossible for an i3, but it's not "good". I've definitely had trips that are at/below that threshold but it's possible that your recent trip(s) was inefficient as far as the car is concerned (maybe AC use this time of year if you're in the US) causing a low range estimate. If you're getting that kind of mi/kWh consistently, I'd look for something like a dragging brake caliper, alignment, or tire issue causing excessive "consumption" prior to looking at the battery capacity.
 
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