General Motors' Chevrolet Volt widened its lead as the top-selling US rechargeable car this year and Toyota Motor expanded plug-in Prius deliveries as Nissan Motor said it was working to boost electric Leaf sales. Sales through to September of battery-only vehicles and those with both battery packs and a petrol engine for added range almost tripled to about 31,400 from 11,094 a year earlier. The Volt, with a record 2,851 sales last month, leads with 16,348 for the year, up fourfold, followed by 7,734 Prius plug-ins and 5,212 Leafs. GM's addition of a discounted lease for the Volt, US$299 a month for a car with a US$39,145 base price, is boosting demand for the model, Jesse Toprak, an analyst at TrueCar.com a vehicle pricing and data provider, said. "I'm utterly surprised people are not lining up to get one at that price," said Toprak, based in Santa Monica, California. "The annual fuel savings alone make this car very appealing." Demand for rechargeable cars, which large carmakers must sell under rules in California and some other US states, hasn't matched initial expectations of Detroit-based GM, Nissan and US President Barack Obama's administration, which targeted a market of 1 million such vehicles by 2015. Nissan, which also added a low-cost lease offer for the Leaf, said designing a sales strategy for electric cars had taken longer than planned. Fisker Automotive's US$103,000 plug-in Karma, with about 1,500 sales this year, follows the models from GM, Toyota and Nissan. Buyers in markets such as California can now lease a Leaf SV hatchback for US$199 a month for 36 months, a bargain based on the car's US$36,050 base price, Toprak said. "Volt has made an ultra-competitive marketplace with the offers they have on that vehicle," Al Castignetti, vice president of US sales for Nissan, said. Nissan, which had a goal of selling 20,000 Leafs in the US this year, has been working with dealers to refine how it markets the all-electric car that goes at least 113 kilometres per charge. The Japan-based company sold 984 of the hatchbacks last month, up from 685 in August. Still, sales fell 4.6 per cent from a year earlier. "We're finally starting to get the dealer engagement," Castignetti said. "We're starting to reach the consumer, the actual consumer for electric vehicles. We're driving more traffic to our dealerships and that's a very good thing." He didn't provide a revised target for Leaf sales. Rechargeable vehicles were "a segment that's in its infancy, and purchases we're seeing now are really fuelled by early adopters", Toprak said. "Until a middle-class family in the middle of the country finds that it makes economic sense to buy one of these cars, you won't see big volume." The Volt, which gets about 61 kilometres a charge, qualifies for a US$7,500 federal tax credit, as does the Leaf. The base model plug-in Prius costs US$32,000, before a US$2,500 federal credit. Other rechargeable vehicles for sale include Ford Motor's Focus EV, Honda Motor's Fit EV and Mitsubishi Motors's i-MiEV battery car. Separately, Toyota said sales of its entire Prius hybrid line doubled to 18,932 last month. Combined Prius sales through September grew to 183,340, surpassing the company's previous full-year record for the petrol-electric car of 181,221 set in 2007. Bill Fay, group vice-president of USToyota sales, said on Tuesday that the company expected to sell as many as 230,000 Prius models this year.