GI3L said:
when the i3 got 22,600watthours.
and 18.800 is usable that 87% right?
so there is a window of just 13% not used for life durability
Correct! The battery management system of the 94 Ah battery pack makes 18% unusable, so for some reason, BMW increased this buffer.
GI3L said:
what i read from other ev's they normally dont discharge below 20% and never above 90%
so they reserve 30%... not 13%
That sounds high, but I've not found any source that compares the reserved buffer percentages for every EV. The original Nissan Leaf has a 24 kWh battery pack, 21.3 kWh of which is usable. That's an unusable percentage of only 11%, less than the 60 Ah i3.
GI3L said:
so how are they expecting the i3 battery will last the 8 years or more?
We don't know BMW's calculation. They probably figured that by the time an i3's battery pack fails under warranty, replacement battery packs would be considerably less expensive, so replacement costs wouldn't be nearly as high as when the car was new. They might do as Honda did with its early hybrids and use rebuilt battery packs as warranty replacement packs. BMW could use "good" modules from wrecked i3's or from failed battery packs to build warranty replacement battery packs (not all modules in a failed back are "bad").
Like other early EV manufacturers, to get acceptable range, BMW had to push the limit of the i3's battery pack due to its high cost/kWh, high weight/kWh, and high volume/kWh, so BMW reduced the unusable buffer as much as possible, even if doing so might shorten the battery pack's usable life. Maybe with the improved volume and charge densities of the 94 Ah battery pack, BMW could afford to increase the unusable buffer to extend the battery pack's usable life without decreasing the range to an unacceptable level.
The tiny 3% high charge unusable buffer that the 60 Ah battery management system uses (i.e., the battery pack can be charged to 97% of its actual maximum charge) might lead to faster degradation if one fully charges every night and allows the battery pack to remain at full charge for hours before driving. So I fully charge only if I think that I might need the full range the following day, and I delay the start of charging so that the battery pack won't remain at the fully-charged state for very long.