CHICAGO – “It's water under the bridge," says Chris Thomason, chief engineer for the Cadillac ELR plug-in electric coupe that goes into production in the fourth quarter and on sale in first-quarter 2014.

Thomason is responding to questions asking why Chevrolet introduced General Motors' first extended-range electric vehicle, the Volt, before Cadillac could market a version of the car. The Volt turned out to be a high-priced ($40,000) limited-edition model, which seems more in character with Cadillac's luxury offerings.

"I won't throw stones,” he says. “But the mentality of management at the time (the Volt came out) was focused on fuel-free technology on a global basis, considering the cost of fuel. We had one global brand at the time, Chevrolet. Now we have two with Cadillac."

Thomason, at a Chicago Auto Show media preview of the car, declines to say how many ELRs that Cadillac intends to produce, other than to say, "We'll build to demand." He waves off any discussion on price.

The ELR will have the same lithium-ion battery pack as the Volt, with a range of about 35 miles (56 km) before needing a recharge of 12 hours using 120V or four to five hours using 240V. Once the battery is depleted, the ELR will run for an extra 300 miles (483 km), after which the generator takes over using gasoline to produce electricity to keep the ELR going.

The ELR does not run solely on stored electricity like new Tesla Model S because they are different cars, Thomason says. “Tesla has a 5-passenger sedan. We have a 4-passenger coupe.

“When you get into a Tesla in California to ride to Arizona, you first get on the Tesla website to find out how many stops you are going to have to make to plug in and recharge. With (the) ELR, you won't have that worry."

Thomason refrains from answering questions about whether other Cadillac models are in line for plug-in power or whether there is a going to be a family of ELRs in the future. Nor does he say whether a convertible is possible.

The ELR is a 2-door coupe, but the car won't have a power sunroof because that would hurt aerodynamics and rob fuel economy.

However, he does say that any technology refinements to the ELR probably wouldn't be shared with the Volt. "Part of being a luxury brand is exclusivity, so that means advances aren't going to Volt."

Thomason also says when the ELR goes on sale next year it will have a national roll out, not a regional debut in selected markets. Based on the technology, Cadillac expects to attract conquest buyers and not rely just on its brand loyalists as potential owners, he adds.