You have to remember that the green bar is just estimating the range based on your driving history. This includes driving style and exterior temperature.
If the Volt starts out at 100% charge, then the top bar represents any point between 91-100% charged, then drops down to 9 bars representing 81-90% charged, etc. The difference between the Volts display and the OnStar app could be just rounding down on the app.
Board of Water & Light
Plug-In Electric Vehicle Community Project
Plug. Drive. Repeat.
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