Thanks vreihen. I'll keep it straight and narrow and work with either the published apps or a mechanic. I dug around a bit more and it does appear that Bimmerlink does battery registrations, although it's not clear if that app supports i3. I have an email into the developer to confirm and...
Thanks for the recommendations of how to replace the 12V battery. I had no idea what the issue was when my car alarm went off and the whole car was dead. Following your instructions above made it easy. I removed the old 12V, found East Penn locally for a new one, then resurrected the car...