It’s fairly straight forward, the unit I have Zappi gives you a daily/weekly/monthly/yearly usage rate so easy to calculate for tax returns.
Does the home charging point tell you how much electricity it has used so you can calculate an appropriate allocation to motor expenses or do you just allocate your entire household electricity bill to motor expenses based on the fact that you need the electricity for the car and hence to work and any other (domestic) usage is merely incidental... obviously as an environmentalist you'd live off grid if you didn't have to charge the car!
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