Like many of you, I’ve read Matt Burt’s recent first drive of the all-electric Renault Fluence ZE. The car looks to be a well resolved, refined contemporary saloon, albeit one powered by batteries rather than petrol or diesel, which is all very exciting for the future of motoring.

Now, I should make it clear at this point that I am in no way against electric cars, but I am against paying a penny more for anything than I have to. So when I came across the figures for charging costs and battery leasing at the end of Matt’s report, I decided to do a few sums.

(I should also state at this point that I failed my maths O-level not once but twice, so feel free to rip the following calculations apart and make me look as stupid as my apparent lack of academic ability did 26 years ago.)

Anyway, Matt says that the Fluence ZE can cost “as little as £3 to ‘fill up’”, which I have no reason to doubt. Matt also tells us that the Fluence’s batteries are leased, at a starting cost of £69.90 a month, but that this cost goes up the more mileage you do. In fact, that £69.90 per month is for a minimum-term lease of 36 months, and up to 60 months.

So, that means you’re paying £70 a month plus charging costs. Those 6000 miles a year work out at 115 miles a week. Assuming, let’s say, an average 80-mile range and £3 per charge to fill the batteries, you’re looking at £4.33 a week in charging, or £17 or so a month, totalling £87 a month combined with battery lease costs.

Let’s say for ease of calculation that diesel costs £6 a gallon. That £87 then equates to 14.5 gallons. Let’s also say we had an economical diesel saloon – a Passat BlueMotion – returning an easy 45mpg. Those 14.5 gallons would take us 650 miles or so a month, or 7830 miles a year. The diesel car is cheaper to run, then, or covers more miles for your money, than the EV.

Or does it? No, it doesn’t, because the Fluence ZE has free car tax and much cheaper servicing costs, so in fact I’d say they’re about the same. But it’s clearly apparent that electric cars don’t equate to free motoring.

But things get interesting if you sign up to do more miles in your Fluence ZE. If you want to do 9000 miles a year, the batteries will cost you £81 a month, plus your charging costs go up too. I’ll skip the interim calculations this time, but the bottom line is that the diesel car will still do more miles for the same money – 9625 of them - but the gap is closing.

Up your battery lease mileage to 12,000 and the Fluence ZE noses ahead – the diesel saloon will only cover 11,395 miles for the same money, with extra tax and servicing costs along the way. At 15,000 miles per year, the Fluence is further ahead still, with our 45mpg diesel trailing at 13,160 miles.

The differences in cost aren’t huge, though. In fact, they’re much less than I would have imagined had I not done the sums. Of course with the Fluence ZE – as with all other pure battery EVs – come the associated headaches of range, charging times and battery life, although Renault’s lease scheme should address the last one of those with replacement batteries should the charge capacity of yours drop below 75 per cent of their original capacity.

But it would also appear that there’s no such thing as a free lunch. If you want to carry yourself and a passenger or two around in the comfort and privacy of your own tin box, it’s going to take a set amount of energy to do it, and that energy is going to cost you what would appear to be a pretty much set amount of money. Unless, of course, I’ve got my sums wrong.