If the generator fails on the road, the car will still be running until the battery drains. Thus, the distance / time to go depends on: - Current state of a battery (the charge level and average discharge rate). - Amount of accessories used (e.g. headlights, board computer running, etc.). - Road conditions. On average, the fully charged battery should let your car run (lights, heating, radio off) another 30-35 miles. The battery capacity matters as well.