[ad#post_ad]At the recent Chevrolet Volt launch GM finally let the skeletons out of the closets and exposed all of the Volt's closely guarded secrets. Among them is the fact that engineers have chosen to use much more of the battery's stored energy than initially beleived.

We had believed for years based on GM statements, that the car would only draw a total of 8 kwh of energy from the 16 kwh battery pack to deliver the 40 miles of EV range. The idea was considerable excess buffer existed in the pack to let it deteriorate over time without sacrificing range.

Through the years of development GM became more comfortable with drawing more deeply from the pack, finding the properly-conditioned cells could handle it. Even with a deeper band of energy use, GM felt it could meet the warranty goal of 8 years/100,000 miles. Also, though executives and engineers won't overtly admit it, it seems they needed more energy than initially believed to the acheive the goal EV range.

This first came out when we recently learned the Volt would use more than 8 kwh.

Now GM finally admits the Volt will actually use 65% of the total energy storage capacity of the battery. That amounts to 10.4 kwh.

The engine generator will turn on once the battery hits somewhere between 20% and 25% state of charge, which equates to 25 to 50 miles of EV driving. When fully recharged, the battery will acutally be kept at a maximum 85% to 90% state of charge.

As the battery ages and energy storage capacity of the lithium-ion cells degrades, control units will widen the percent state of charge band to continue to deliver the range goal.

By 8 years/100,000 mile when the battery warranty ends, GM expects the car's range to be reduced by 10 to 30 percent in the worst case. Some customers will experience less degradation. The car can continue to drive beyond that point, but range will continue to contract.

It was recently reported that the California Air Resources Board (CARB) classified the Volt as a ultra-low emissions vehicle or ULEV. This is the same as a 1.8L Honda Civic, for example. Less carbon emitting and more stringent designations include (super) SULEV, and advanced technology partial zero emission vehicle (AT-PZEV) given to the Prius and Insight. The most stringent is the zero-emission (ZEV) designation given to pure electric cars.

The ULEV designation does not, however, take into account the Volt's electric driving operation, it only looks at the charge sustaining mode operation. GM will seek a new (enhanced) EAT-PZEV status next model year, by offering the required 10 year/150,000 mile warranty that CARB wants to consider electric operation. To achieve that warranty, apparently "certain kinks" have to be worked out Volt director Tony Posawatz told the Times .