You 100% need WiFi for the maps update.
To add some more data, some entries from my car's logs:
Code:
"target_version":"NA-180906-1605","size":5506434476,"max_wifi_kbps":10000,"max_cell_kbps":0
Code:
nav_us start/resume download because conditions met: (BASE CONDITIONS) charging || ! sleepenabled || ( ! charging & (sleepenabled & sessiontime < 3600))
So, the latest maps download is ~5.5GB, and gets downloaded on WiFi only at a maximum of ~10mbps.