Video: BMW i3 Range Extender review All very convenient if you plan to build an electric car, but don't forget that BMW is also continuing with its development of internal combustion engines. Indeed, it freely admits it is a horses for courses approach, and so if you're an early adopter then an i3 with BMW's 360-degree ownership package (which includes access to 85 per cent of the UK's public charging points and preferential rates for BMW car hire schemes), might well have enough ingredients to appeal. As other car manufacturers have discovered, however, no matter how short somebody's daily commute might be, they are still going to get range anxiety when told they can only drive 80-100 miles between eight-hour recharges (reduced to four hours if you use a 32A BMW wallbox). Which is why, for an additional £3,150, BMW will sell you a range extender for your i3 in the shape of a 650cc, 34bhp motorcycle engine mounted in the rear of the car along with the electric motor, and acting as a generator to maintain (but not add to) the battery's state of charge. The theory is that it doubles the i3"s range, and should you need to go further still then you can keep topping up the nine-litre fuel tank (CO2 emissions climb from zero to 13g/km). Back to that motorway journey. The idea was to drive a return trip from London to Folkestone, which at 70 miles each away would be impossible in most other electric cars. Even so, I was slightly surprised to have run the lithium-ion battery flat not on the return leg, but five miles before even reaching the coast, meaning the i3 had made it just 65 miles on a full charge. Still, the range extender kicked in and, with what sounded like a lawnmower humming away in the boot, I reached my destination. This being a connected car, I used one of its two tablet-style screens to search for a charging station, figuring it would be good to get a little juice back into the eight battery modules before setting off for London again. Only there aren't any public charging stations in Folkestone, or at least none that our car recognised. This, I thought, is exactly the kind of situation the range extender was invented for. However, it soon became evident that, thanks to its tiny fuel tank, driving in range extender mode isn't unlike driving on a petrol or diesel car's reserve light - i.e. uncomfortable. Even a precautionary pre-motorway top up (5.1 litres and a day-before-payday-esque transaction of £6.57) only gave a range of 60 miles. I thrummed along at 70mph, but it soon became clear that at this kind of speed our comfortable range between fill-ups was more like 40-50 miles. Still, it was impressive how, even when it says it's flat, the car maintains enough battery power to give an instant shove of torque. Only if you really run it down, which you'll have to try pretty hard to do (or so I'd been told), would you compromise the performance. Which is what happened next. I'd just come through a heavy but localised rain storm on the M20 when the i3 started to slow. It was a gradual process, from motorway cruising speed all the way down to 44mph. By this time I was travelling up a slight incline and had effectively become a slow-moving obstacle. Lorries were catching me with quite frankly terrifying closing speeds. It was three or four minutes - which was long enough to make me consider pulling over - before the i3 recovered; just as slowly as it had lost speed, so it crept up. "It's not a limp-home mode as such," a BMW spokesman later told me, "but once the charge runs down to five or six per cent and the range extender cuts in, if you keep driving at 75-80mph it can't maintain the charge." Rather than damage the battery by running it completely flat, the i3 had restricted our performance. What I should have done, it transpired, was engange the range extender when there was still 30-40 per cent charge in the battery. Still, the car had covered my mistake, albeit in a slightly alarming fashion, and the remainder of our journey back into London went without a hitch (save needing to add another 7.5 litres of petrol). Putting aside the loss of power, the i3 was a delight to drive. Thanks to its carbon-fibre passenger cell, it weighs just 1.3 tons, which means that 168bhp from the electric motor is enough to give it strong performance (evidenced by a sub 8sec 0-60mph time). It is also very refined, rides well enough and handles beautifully, thanks to its even weight distribution and low centre of gravity (the battery is mounted in the aluminium chassis). As for niggles, a boot that's too small to carry a child's buggy, thus removing some of the i3"s usefulness as a second car for many people, blots the i3"s copybook, as do a couple of small inconsistencies in interior build quality. But you counter that with the thought BMW has put into this project, right down to the use of sustainable power sources for the factories where the carbon-fibre and the cars themselves are made. Throw in the tiny running costs of an electric car and it is a true feel-good proposition. Amazingly, even the £34,000 price (from which you can deduct the £5,000 plug-in grant) seems almost justifiable when you look at the supercar-style construction technology. What it is not, however, is a five-star car. How could it be when, user error or not, it can't guarantee it'll be able to maintain a safe motorway cruise even when it's got a full tank of fuel? No, what this i3 Range Extender represents is a big step forward for electric cars, and an extremely desirable urban runabout. If it suits your lifestyle and you like the design, then you'll almost certainly love the i3. But even in this Range Extender guise, it is not the panacea some are suggesting. BMW i3 Range Extender Tested: 22kWh lithium-ion battery driving an AC electric motor, plus 650cc Range Extender, rear-wheel drive Price/on sale: From £28,830 including plug-in car grant/now Power/torque: Electric motor: 168bhp/184lb ft. Range Extender engine: 34bhp/39lb ft Top speed: 93mph Acceleration: 0-62mph 7.9sec Range: 100-180 for Range Extender) CO2 emissions: 13g/km Verdict: Great fun to drive and a big step forward for electric cars, but even with the range-extender option this is not a car for those who regularly undertake long journeys. Early adopters will love it, but the cynics will remain.