The batteries hold ~22kwh. Shouldn't that be sufficient information when you multiply this by the price per kwh (e.g. in Germany ~22-25 Eurocent).
--> ~5.20 EUR per full charge == 160 km. ==> 3.23 EUR / 100km.
Actually it might be even a little lower, since the i3 (an no e-car does) uses the whole capacity of the battery. In case of the i3 only 18 kwh are used.
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