GM U.S. Sept sales "looking fine:" exec

FRANKFURT (Reuters) - General Motors Corp's GM.N U.S. September sales are "so far looking fine," GM's product chief Bob Lutz said on Monday.

While acknowledging that it's early in the month, Lutz said there is "no cause for worry."

"We are about where we thought we would be," Lutz said on the sidelines of an event ahead of the Frankfurt auto show.

Lutz also said the automaker might lose money on the Chevrolet Volt -- an electric vehicle it plans to produce in 2010.

"This is a venture into the unknown," Lutz said. "I think we are fully resigned to the fact that the first generation of the Volt may not make a lot of money for us. In fact it may lose money ... We just don't know yet."

Automakers have said lithium-ion battery technology remains the biggest challenge in producing a plug-in vehicle as they try to lower the cost of the batteries and increase their power and storage capacity.

"We have a pretty good handle on what the vehicle portion is going to cost," Lutz said. "What we don't know is the cost of batteries."

The current generation of lithium-ion batteries, used in devices such as laptop computers and electronic devices, also has a tendency to overheat.

Lutz has said GM is exploring options that would allow consumers to lease the battery when buying the vehicle in order to bring down the sticker price.

Unlike earlier gasoline-electric hybrids, which run on a parallel system twinning battery power and a combustion engine, plug-in cars are designed to allow short trips powered entirely by the electric motor, using a battery that can be charged through an electric socket at home.

GM is designing the highly-anticipated Volt to run 40 miles on battery power alone, reducing or even eliminating the need for drivers to fuel up an on-board gasoline-powered engine provided as a backup power source.

(Reporting by James Kelleher; writing by Jui Chakravorty)