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You can tell the car to display the available range in miles or percentage. In the settings screen one is called Distance and the other is called Energy. This setting is per Driver Profile. My wife has her profile set to distance and I have mine set to Energy. The App will follow whatever is currently displayed in the car.
Some third party apps also allow you to see and set precise percentages. I use the app "Remote S" to set it in 5 percent increments to satisfy my ocd about it .
My navigation shows what the battery percent would be when i reach the destination. So i just plug an address pretty to close to my location and hit navigate. The directions list the % battery left.