Extended Range Battery Pack

Battery advancement in terms of energy capacity per unit weight and/or volume has a lengthy development cycle to verify that changes to electrode and electrolyte formulations don't introduce unforeseen flaws that would compromise the design. The battery box is pretty big already and not likely to grow in size. This means that the battery technology must be advanced to gain meaningful added capacity. It is estimated that a 135 kwh pack of the same or smaller size than the current pack would yield a 500 mile range for a car that weighs 3000 to 3300 pounds and that has the same or lower drag coefficient than the current Model S. However, optimal average speed on a road trip would be obtained by driving about 75 mph between charging stops that are 300 miles apart so that the "upper" 40% of the battery capacity would not have to be used between SCs in order to minimize recharging times. Not going to happen for a long time IMO.

The new scalable 90kWH battery isn't an add-on to your existing battery but a total replacement for ~$22,000. That's not what Elon said in his release letter but it's not surprising that he says one thing but means another.

The new 400+ miles car is coming in the future. I may not be alive then, since they are consistently 2-3 years behind schedule for new releases.

I personally feel deceived about the swappable battery. This is what convinced me to go with Tesla as opposed to another car. Superchargers suck; way toomuch time.  I wanted an option I could pay for that would equal a tank of gas.