It's electric, of course: no concept is complete these days without some batteries tucked away somewhere. The Emerg-e has a substantial bank of lithium iron phosphate cells feeding power to its twin rear-mounted motors. Together they can spit out more than 400bhp and up to 1,000Nm (740lbft) for periods of up to 30 seconds, which incidentally is long enough to reach 130mph from a standing start. If 60mph is your goal, just four seconds should cover it.
At the other extreme of watching the clock, it'll take 10 hours to recharge the batteries from a domestic plug, and after that they'll only carry you about 30 miles -- or quite a bit less if you keep lighting up the 20-inch rear tyres. Fortunately there is an engine on board to provide additional electricity without the wait.
It's probably best to dwell on the fact that the engine was developed by Lotus, rather than pondering its puny 1.2-litre, 3-cylinder specification. Lotus's compact unit was developed specifically for range-extended cars, however, and is both light and highly efficient at turning petrol into electricity.
What it can't do, however, is supply enough power to sustain high speeds for long periods. The little Lotus 1.2 can produce a steady 35kW, sufficient to push a big car like the Emerg-E along all day at the legal limit but not much faster. Infiniti doesn't give a figure, but somewhat less than 90mph would be the likely maximum cruising speed. Going faster will only happen while there's charge in the battery.
But when it looks like it looks, and delivers a planet-pleasing 55g/km of CO2, who cares if you have to dawdle a bit between bouts of 400bhp fun?