Seeing "Replace Battery" on the screen in your Tesla produces a little anxiety, I can attest to that. This message popped up on my Model 3 yesterday. Luckily, the devil is in the details - the 12V battery needs to be replaced, not the battery battery.
A few taps in the app last night and I scheduled an appointment for first thing this morning...and now I'm sitting in the service center waiting for the tech to complete the job. Normally I'd replace a car battery myself, but the price they quoted me is ridiculously cheap...and I don't know how to access the 12V in the 3. So, service center coffee for me this morning.