Thats the way I’m working it out, except the charging cost, where I put a % figure of the remaining charge into a spreadsheet, which then calculates cost to charge on the difference i.e inset 12(%) it calculates charging on the kW’s needed for the remaining 88%, with the sum (100 – x%) = x% x 13.8 / 100 x 0.22, its simple because it automatically calculates % remaing I put in.
I have just been to B&M’s and partly back total 6 miles, on the remaining 1 mile electric range left, the car managed 4 miles on electric and another half mile after it showed 0 miles left 🙂
P.S think of HEV mode as a full hybrid, rather than just charging the battery, with the added advantage of switching back to electric mode every now again for 2-4 miles.