One of the problems with electric cars is that, like some smartphones, they run out of power too quickly and need to be plugged in to recharge. But what if battery-powered cars could recharge themselves wirelessly, while parked at the supermarket, or even while driving down the highway? That day may arrive sooner than most would expect. Start-up tech company HaloIPT has developed a prototype battery-powered car that recharges itself wirelessly, one of scores of 'green' car solutions currently on show in Shenzhen. An unusual mix of scantily-clad models, motorheads, academics and techies were on hand yesterday for the formal opening of the 25th world battery, hybrid and fuel cell electric vehicle exposition (also called EVS-25), a rotating global conference last hosted by the mainland in Beijing in 1999. Green cars have come a long way in the past 11 years, a fact demonstrated by the plethora of prototype and production-model electric buses, bicycles, sedans, SUVs, scooters, trucks and golf buggies from a range of foreign and domestic manufacturers that are on display. But many of the challenges facing electric cars are the same today as when they were first introduced to the world more than 100 years ago, only to be usurped by the internal-combustion engine. Battery packs capable of storing enough power to match the performance and driving range of gas guzzling engines are usually either prohibitively expensive or prohibitively large (often weighing 300 to 500 kilograms). This is where innovations like HaloIPT's wireless charger get interesting. By allowing cars to charge more easily, and potentially continuously, the batteries that power them would not need to be so large - and thus they would be cheaper. That could bring the overall cost of green cars down to something closer to that of their petrol-powered cousins, while eliminating 'range anxiety' over the distance driven between recharging points. 'The goal is to make electric cars cheaper and alleviate concerns about recharging,' says HaloIPT chief executive Anthony Thomson. HaloIPT, which was spun out of New Zealand's University of Auckland and received start-up funding from global engineering and design consultancy Arup, is one of several companies working on a technology called inductive power transfer. IPT is currently used commercially to charge some electric toothbrushes but is more often employed industrially to power machines in automated manufacturing. For the car industry, HaloIPT has installed an IPT system in a Citroen C1 converted to run on a lithium-ion battery. A sensor mounted on the underbody of the vehicle receives electricity from a mat on the ground that is plugged in to a standard power supply. According to Thomson, the charging mat can transmit electricity to the sensor at a distance of up to 40 centimeters - regardless of whether there is ice or snow between them - allowing the mats to be buried in household garage floors or corporate parking lots. The 15 kilowatt-hour lithium-ion battery in HaloIPT's prototype can be fully charged in about five hours on a standard household outlet, which is comparable to most plug-in electric cars with a similar-sized battery, Thomson says. But going wireless means a car could potentially charge while on the move, be it an electric taxi queuing in a rank or driving down a street with charging mats under the asphalt. 'Nirvana for us is doing this while the car is moving,' Thomson says.