I see Motability’s assumption is based on easy maths 0-100%, when in reality you mostly charge from 20-80% and thus need to know what 60% of a given battery size, to work out the cost to charge.
The iC1 has a 64.7kW useable battery – 60% of 64.7 = 38.82kW’s needed to charge from 20-80%
Price per kWh x (60 x 64.7 / 100) /100