(I did send in email asking about other possible benefits and will update if I learn something surprising!).
I got a call from Tesla today. As you can imagine, they don't have all the details in place yet, but they tried answering my questions as well as they could. Here is how they think things look so far (I did ask for permission to post this; they were OK as long as I noted that not everything is final):
1. The new pack will include a 3-year warranty. They hope to have an additional extended warranty available for purchase, but they do not have details on that yet (including whether any sort of extended warranty will be available here in WA; we can't buy the other extended warranties)
2. The PEM modifications are small, likely just doing something like allowing for higher voltages during charging. The piece they add will have a "small" warranty, but the rest of the PEM will not.
3. The battery will be heavier, but the person I spoke with had not been told how much heavier.
4. The heavier battery will not slow down the car, because the bigger battery will provide a little more power. It sounds like they should just about cancel each other out. In fact I wouldn't be surprised if they made it work that way on purpose (though that is pure speculation)
5. You are expected to turn in an old battery when you buy this new one. However, they give no credit based on condition, so it doesn't seem to matter what type of shape the battery is in. If you have to tow in the car with a non-working battery, that sounds fine. Richkae's idea (sell his good battery to somebody with a bad battery; then trade the bad battery in on a new one) might work. Of course I would have a long talk with the service center doing the work to make sure before counting on this!
6. This is not a limited-time offer. Of course they can't guarantee they will offer the same deal forever, but they plan to offer this going forward. So if the timing isn't right to upgrade now, you can upgrade later.
If you have a bad battery or need more miles now, it is great they are offering this. But for those of us that have good batteries and don't need more miles, waiting until you do need it seems like a reasonable course of action.
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Is most of the cost the cells at this point or the labor since there are so few of these packs and I'd imagine mostly done by hand?
Tesla isn't saying, so I don't think anybody knows for sure. But I imagine that cells are the majority of the cost, though labor still a significant percentage on the Roadster packs.