Well, one thing for sure: If you have 100K+ miles on an ICE, and you had a major problem with, say, the engine - it is not uncommon to have non OEM parts to replace - say - a rod or a cylinder or something, and BMW/MB/etc. doesn't really care as they are out of warranty - so one may opt to go to a Euro-auto-haus and fix their car in their own chosen fashion.
As EVs become more mainstream, and 7-10 years down the road, someone will have a company that - say - offers to replace your 85kWh battery with a non-OEM 170kWh battery pack, taking the old one, placing it vertically in your garage, hook it up to your breaker, installing a computer interface, and giving you a backup "generator" for power failures.
All this, for less than the price of what Tesla would offer.
Certainly not outside the realm of possibility. I agree with Johan ... don't assume that 200kWh would work, and also that batteries follow Moore's Law.
Point: my crystal ball is in the shop, and my psychic beanie baby has been sick lately, and nobody really knows where the future of batteries, Lithium, A123, etc. are headed. I, for one, am interested to see.
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I asked my product specialist about upgrading to a bigger battery capacity in the future (i.e. 8 years) and got this response:
"Batteries will not be upgradable in the future.* As technology improves, their range may increase, but it will still be the same size battery pack.* You will be required to replace battery packs like for like."
I am shocked by this, as I don't see any technical or logical reason for this limitation. I am also confused how the same capacity batteries could provide increased range.
I also refer to our Summer experience with PS, DS, and OE personnel and their verbiage (I would guess he meant, "since we assume you will buy from us, you will get what we make, and we won't support a different size"). Again, all speculation