> It's not like you can replace the battery in your phone with a larger one.

That was totally a thing for phones in the past. Depending on the model you could get a larger pack that had a bulge on the back of the device to have extra battery time. There was a similar thing with a number of laptops.

I do agree its kind of a questionable thing on something like a car. I imagine packaging concerns would really get in the way of adding a bit extra.