If you go by the book (topix/workshop manual), the battery is supposed to be replaced after an SOS call, so looks like you're going down the right path given your last message. But as I said in my last post, I don't believe the system automatically re-calibrates itself, so you need to get Jaguar to reset it when the battery is replaced to remove the warning - so possibly not something you can do yourself anyway.
As for the TCU location - maybe the location under the steering column is for vehicles with the basic Incontrol system? (as the location I posted is for if you have Incontrol Touch Pro)