I absolutely agree with you. Tesla will use batteries for their Semis, because its the variable they can control.
I also agree they have a clear path to doing that affordably.
I also agree their battery costs are (probably) less than we know, and your $85/kWh figure may not be that far out of line. You said conservative. Using the information that is publicly available, and without assuming anything, a conservative estimate should be more like $135/kWh was all I was suggesting. I'm personally expecting real world GF cost to be around $75-100/kWh.
I agree driverless is part of the plan, and relatively easy to solve, but I don't think regulators will allow it for quite some time, so I believe a Tesla Semi will be able to make its value proposition without being driverless.
If you paid attention to the formulas I used, the hours without stopping was only used to estimate a reasonable pack size. Pack size doesn't change the economics of it in terms of fuel consumption. I wasn't actually suggesting the economics don't work, necessarily. I was just trying to use physics to come up with reasonable estimates of what it would take to do it. No amount of battery technology or intelligent design will change that you need a certain amount of power to move a big vehicle through the air and across the road surface.
Conventional - Sleeper Trucks For Sale
This seems to suggest that the ballpark price range of existing diesel sleeper cab trucks is $130-150k USD. As others have suggested, the trucking world is all about the dollars and cents. You wont sell a more expensive truck unless you can make an economic argument for it.
Several searches comes up with long-haul trucks averaging about 100,000 mi/yr. Lets say 5 year life of the truck (though its probably closer to 10 year). 500,000 mi. 2014 regulations state new sleeper cab trucks have to achieve at least 7.2mpg. So lets base on 8mpg. 500,000 mi / 8mpg = 62,500gal of fuel.
62,500 gal of fuel * $2.50/gal = $156,250 in fuel costs
Cost per mile work sheet for Owner Operators
suggests about $12,500 in repairs, maintenance and tires per year is $62,500
plus the $150k cost of the truck, is $368,750 total cost of ownership for 5 years.
I can't find a new price, but used DD15 Detroit Diesel with low mileage goes for around $15,000 on used markets. Lets estimate $25k new.
I assume you need to go 11 hours straight, because recharging takes time, which can be done while the driver sleeps.
So if the rest of the truck is worth around $125k, Based on yesterday's math, I needed around 1000kWh of batteries to make it run 11 hours.
1000kWh * pack cost of... $100/kWh assuming decent gains from GF is a $100,000 battery.
That would make it about a $225,000 truck.
500,000 mi @ 1.61kWh/mi = about 805MWh. 805MWh * $40/MWh wholesale electricity cost is $32,200.
Tires and maintenance costs will probably be around the same price, so $62,500
That totals to $319,700 total cost of ownership for 5 years.
Certainly seems like it could be viable.