As there was a question regarding battery longevity, I ride a 2014S that I purchased new in 2015, and, as the 5 year warranty (and 45k miles) was coming up, the battery began to have increasingly strange behavior, and noticeable loss of range wrt new. My guess was there was a bad cell, but I didn't attempt to diagnose this further, as Zero was good enough to replace the battery under warranty after confirming the impairment. As the original (2014) battery was no longer produced or available, a present day (2020) battery was installed (a net upgrade in capacity). This change in battery details apparently was a bit complicated, given the various interactions I had with the service department, and required several consultations between the service department and Zero (plus a few extra trips back to the service department, over a couple of months) to get everything working perfectly.
For my primary use case of commuting ~40 miles round trip per day, I would have kept operating the original battery for as long as possible barring a catastrophic failure, but I am content to have a battery without many years and miles so that I can do longer distance errands in addition to commuting. I have no notion of what the cost for installation (battery + shop time) would have been, but almost certainly more than I would have willingly parted with!