General Motors succeeded in creating some rare buzz through its cryptic, logo-less “230 8-11” ads (the “0” was a smiley-faced electrical outlet). Now comes the buzz-kill. The company boasted on Tuesday that, under a new US government methodology, its Chevrolet Volt would be rated at 230 miles per gallon – the first vehicle ever to crack triple digits. Using the same calculus, the all-electric Nissan Leaf, also set to be introduced in late 2010, does infinite miles per gallon. By counting only the portion of a typical daily drive using petrol rather than converting the calorific value of electricity, GM has won a marketing battle. It may yet lose the war for market share.

On one hand, the Volt, technically an extended-range electric vehicle that uses a petrol charger after about 40 miles, will be more practical than all-electric competitors. The Leaf and a vehicle already produced by China's BYD – and slated for US sales in 2011 – get 150 and 50 per cent more miles, respectively. But the Volt's total range is a far longer 300 miles. Conversely, the Volt may cost 50 per cent more than either competitor, even after generous subsidies of $7,500. Then there is hybrid champ Toyota, which will beat both GM and Nissan to the US market with a plug-in hybrid later this year.

Improving technology may mean the age of mass-market electric cars is nearly here – Nissan predicts they may snare 10 per cent of global sales by 2020. But, in spite of generous subsidies, American manufacturers have lost the technological lead. Meanwhile, their home market, with cheap petrol, long commutes and expensive labour, makes a poor base for gaining critical mass. Gaudy marketing claims aside, those betting on Detroit's dominance of electric cars should prepare for a shock.