Simple question really, what’s the best way of calculating how much it costs to charge a particular car?
I know there’s a similar post here:
However if we already know the battery capacity, let’s say 30kWh, can we not just multiply the cost per kWh that we get from our energy companies? Or is it not as simple as this due to the charge tapering that occurs once you pass 80%?
@osbrook you’re much more up on things like this, maybe you could explain 
There are a couple of methods for a Twizy or a car using a EVSE brick. Use the @ecofunkytravel suggested Plug in Power meter.
Or for a more generic route for all cars.
Take the usable battery size in KWh and multiply by the cost of Electric. Allow between 5 and 10% for losses.
So a Twizy battery Say 8KWh (allowing 10% for losses) times peak rate 15p = £1.20 for a absolutely full charge. Usually the battery isn’t empty.
or a Leaf 24KWh battery (only 22KWh usable) but 25*.15 = £3.60
So it pays to use cheap rate electric and or Solar. Twizy comes out at 40p on E7
All depends on the rate you pay for Electricity.
@james mentions Tapering. Tapering is where the rate that the battery can absorb the charge drops off. ie. a battery on a Leaf may charge up to 80% in 30 minutes using a lot of current (watts) and then draw less power for then next 2 hours. However the overall power draw will still be the same 24KWh. 19.2KWh going in fast and the last 5 goes in slowly. Still only 24KWh.
Great, thanks for the explanation.
Ahh yeah! 
At the risk of coming across as an awful EV wet blanket, however much the electricity costs you will unfortunately be swamped by the cost per mile in battery rental/degradation. I think this is still true for all EV’s, but hopefully won’t always be. And despite that, they’re still (most of them) cheaper to run than most conventional cars, if perhaps not quite as much cheaper as some enthusiasts and EV marketeers claim.
But operated “right” they should be much kinder to the environment and your fellow man!
Thanks for the insight