My initial March 2017 S100D battery lasted until March 2023. 6 years almost to the month. 90k miles. Austin, TX so some moderate heat and moderate cold, nothing outrageous. Garage kept. I do not use sentry, summon standby.
Just changed mine original battery also, 6 years to the month. Though mine is a late 2016, was a showroom demo car with 400 miles when I bought it, so battery was actually more like 6.5 years old, as unlikely they changed it out before I bought it as first owner.
Mine started to get the "schedule service warning", I thought it was because I'd gone on a 10-day trip, and the HV battery had drained from 70% to below 20% near the end, so I thought maybe it stops recharging the 12V after the HV battery got below 20%. But I checked my Teslafi logs, and it looks like the car stopped sleeping normally about 2 days BEFORE I left on the trip. So it's really the other way around, the dying 12V battery causes the car to not sleep properly, and that increases the phantom drain while I was away. Saw a similar thing with a relative's Model 3, where it was the 12V that caused increased phantom drain along with other weird behaviors, and the 12V warning only shows up weeks later.
New 12V battery (AGM according to the invoice) was $165, plus $50 for labor via mobile service (slightly cheaper than some reported here for older Model S, maybe because easier access on my facelift model). As others stated, you schedule via the app for the service center, but then they reach out and change it to mobile service with usually an earlier date - in my case they scheduled the very next morning.... Also had the 12V replaced proactively on my 5-year old 2018 Model 3 on the same visit; comparatively, $85 for the (lead acid) battery and only $25 for labor, he swapped it so quickly I thought he was putting the new one back in the cardboard box he'd just took it out of. At these prices for OEM battery and mobile service, I'll never bother doing 12V replacement myself after 20+ years of DIY on all my previous cars.