Volt Misses Another Goal: Battery To Discharge Deeper Than Planned

Although the finished product works well enough, it’s also becoming increasingly apparent that the Volt missed two key project goals. GM’s oft-stated promise that the Volt would achieve 50 mpg in CS mode is history. The fact that GM felt the need to optimize the fuel consumption of the Volt by using premium (required, not just recommended) indicates how rather inefficiently its serial-predominant hybrid system works. It’s not a matter of ragging on about that; it’s just a surprise to those of us who argued endlessly which system (serial or parallel) was more efficient.

And now another long held Volt assumption is deflated. Based on GM statements made during the Volt’s long development, the universal understanding was that the Volt would use 8 Kwh of its 16 Kwh battery pack to achieve its 40 mile AER goal. It now turns out that 10.4 Kwh will be utilized. Sounds like small potatoes, but there are three not insignificant consequences as a result:

The very immediate and obvious one is that it will take more electricity to recharge the Volt. Given the losses of conversion at the charger and in the battery, it will probably take 12 to 13 Kwh of metered electricity to recharge a depleted Volt battery, so that the electric “fuel” costs in calculating the Volt’s operating costs need to be increased by some 20%-25%.

The more serious issue is that this deeper rate of discharge will stress the battery to a greater degree. Unsurprisingly, GM says, and presumably believes, that this is not a significant issue, and has confidence in the battery’s long-term health over its projected life. GM has said that the battery will lose between 10% to 30% of its capacity during the 8 years/100k miles of the warranty period. Whether the consumer or GM are hurt more if the Volt battery eventually turns out to age more rapidly is unknown, but it does increase the odds of there being an impact as a result of the deeper discharge.

Why was this change made? The Volt wouldn’t have met its nominal 40 mile AER without it. This and the Volt’s lower gasoline economy are interrelated. Both early Volt goals (40 mile AER on 8Kwh and 50 mpg in CS mode) were not met, because the Volt turned out to be less efficient in both modes.

Whether that’s the fault of excessive weight (some 3800 lbs), or less-than sterling aerodynamics (Cd: .28, same as a W124 Mercedes of 25 years ago), or other inefficiencies, is not known. Yes, the Volt works, just not as efficiently as hoped for, by both its maker and those that have followed its development.