I agree with AnOutsider, actually. How do you have any idea what the base battery pack "costs"? Up until yesterday, all we knew was that we could get a 160 mile battery pack for $57k for the base car, but I've seen no information that indicates that the cost of that pack is $10k, only that the extra miles (240 and 300) cost an extra $10k respectively. Actually, if I had to guess I'd assume that the base 160 mile pack costs more than $10k as part of the total $57k...
True, but that only makes a trade-in 5 years later even financially worse as it's a larger sunk cost that's going to have a larger depreciation. Let's run some numbers for fun.
Base costs today. The 160 is rolled into the price, so I'm choosing an arbitrary price for the base battery. If it helps, pretend you could buy a base model at a reduced price if you got it without a battery.
160 = $10,000
240 = $20,000
300 = $30,000
Day One trade-in: You give Tesla the 160 and $20,000 and walk away with the 300.
Lets's say battery prices drop 50% over 5 years and assume degradation and tech has dropped your battery's trade-in value to nothing:
160 = $5,000
240 = $10,000
300 = $15,000
Year 5 upgrade = Trade in the 160 for $0 (it's worthless), buy the 300 for $15000. So, on year 5, your cost for the upgrade is $15000 rather than the initial upgrade cost of $20,000. Not a big savings despite the 50% battery price drop. If Tesla does buy back the old battery for something other than peanuts, then that helps.
Now, let's assume the Day One costs are:
160 = $30,000
240 = $40,000
300 = $50,000
Same day one trade in scenario. You trade in the $30,000 160 battery and get a 300 for another $20,000.
Year 5 changes quite a bit though.
Trade in the 160 for $0 (it's worthless), buy the 300 for $25000. So, on year 5, your cost for the upgrade is $25000, more than what the original upgrade would have cost you! Again, any value in the original battery helps.
The more expensive you assume the base battery, the worse off you are upgrading years later because of the value lost in the depreciation of your original battery. If there's some reason to believe a 5 year old battery would hold it's value, then things change, but if the assumption is that battery tech is going to make batteries cheaper than it also means your 5 year old battery depreciates heavily.
The base 160 mile pack loses value the same way the doors, windows etc.
Exactly. If you came back 5 years later and wanted to upgrade your door, you're going to pay full price for the new door because they don't want your old door back as trade-in after 5 years. If you'd done it at the time of purchase, you're not buying a brand new door, you're paying the upgrade difference.