Learned from Tesla telephone support 12-16-2015:
Up to 5 miles of range for each charging minute may be available at a Supercharger. However, capacity is provided to pairs of charging "slots" and if one of the slots is is active use, the "companion" slot may (will?) not find that rate of charge to be available. Slot "pairs" are identifiable by number and letter (e.g., 3A is paired with 3B), but note that paired slots may or may not be physically adjacent to each other.
When arriving at a Supercharger, consequently, it is advisable to select a slot whose "companion" is not in use. If many slots are occupied, it may be necessary to share a companion pair with anther Tesla, in which case you may find that the charging rate available is substantially less than 5 miles of range per minute of charging time.
If charging is underway at two companion slots, rather than dividing the capacity equally, as one might expect, the system gives preference to the first car. Experience indicates the following to be true: If the first car of a pair of cars sharing two companion slots completes its charging, the charging rate for second car is not automatically and immediately increased: The owner of the second car must "stop charging" and "start charging" to take advantage of the additional capacity made available by the first car's having vacated its slot. (Stopping and starting charging can be carried out on the touch screen display -- controls-settings-charging -- or remotely by utilizing the mobile app.)
Up to 5 miles of range for each charging minute may be available at a Supercharger. However, capacity is provided to pairs of charging "slots" and if one of the slots is is active use, the "companion" slot may (will?) not find that rate of charge to be available. Slot "pairs" are identifiable by number and letter (e.g., 3A is paired with 3B), but note that paired slots may or may not be physically adjacent to each other.
When arriving at a Supercharger, consequently, it is advisable to select a slot whose "companion" is not in use. If many slots are occupied, it may be necessary to share a companion pair with anther Tesla, in which case you may find that the charging rate available is substantially less than 5 miles of range per minute of charging time.
If charging is underway at two companion slots, rather than dividing the capacity equally, as one might expect, the system gives preference to the first car. Experience indicates the following to be true: If the first car of a pair of cars sharing two companion slots completes its charging, the charging rate for second car is not automatically and immediately increased: The owner of the second car must "stop charging" and "start charging" to take advantage of the additional capacity made available by the first car's having vacated its slot. (Stopping and starting charging can be carried out on the touch screen display -- controls-settings-charging -- or remotely by utilizing the mobile app.)