ELECTRIC vehicles are expected to stream onto the roads over the next few years, but some drivers may be put off by fears that they could be left stranded if their battery runs out of charge.

Zafer Sahinoglu�at the Mitsubishi Electric Research Laboratories in Cambridge, Massachusetts, and colleagues, think they have found a way to prevent this. They are developing a network of portable charging stations, which can be moved to wherever the demand for recharging is greatest.

To determine where the stations are needed, in-car sensors would monitor the level of charge in the battery and periodically report this to a central operations centre, which would flag areas where most cars run low on juice. The stations can then be deployed wherever the low-charge "hotspots" are at that time. Just five mobile stations would be needed to cover 100 electric cars on a 100-kilometre stretch of highway, the team says.

The roaming stations could be charged up from the mains at night, and then discharge their electricity to cars during the day, they say, reducing the load on the electricity grid at peak times. The team will present their idea at theVehicular Technology Conference�in Ottawa, Canada, next week.