Yes, I too think 85 kWh is possible but they are not doing it because it would make the Model S look bad. Just by looking at these Model 3 range numbers that I calculated, you can see why they went with the 75 kWh battery:
Model 3 75D: 297 mi EPA rated range
Model 3 P75D: 281 mi EPA rated range
Model 3 85D: 330 mi EPA rated range
Model 3 P85D: 313 mi EPA rated range
Model S 100D: 335 mi EPA rated range
Model S P100D: 315 mi EPA rated range
The 0-60 time of the Model 3 P85D might be the same as the Model S P100D. If both cars had the same range and performance, fewer people would buy the Model S P100D instead of the cheaper Model 3 P85D. That's why they went with the 75 kWh.
Here are some details about this subject:
- The Model 3 will have a performance version. Elon confirmed Ludicrous mode here.
- 75 kWh for the Model 3 was confirmed by Elon here.
- The Model 3 75D is expected to have around 300 mi EPA rated range based on this screenshot.
By the way, some people might think that whatever Elon had said
here, people would want more. If he had said maximum 80 kWh, people would say why not 90. If he had said maximum 85, people would say why not 95? You might think that I'm doing the same thing but that's not true. I predicted 75 kWh now and 85 within 2 years a few months before Elon tweeted about the 75 kWh. See my message
here from Dec 2016. I have since adjusted my range calculations. I'm now expecting 297 mi EPA for Model 3 75D.