I used to use Google Sheets to geocode for Leaflet maps, but:
You can display Geocoding API results on a Google Map, or without a map. If you want to display Geocoding API results on a map, then these results must be displayed on a Google Map. It is prohibited to use Geocoding API data on a map that is not a Google map.Geocoding API Policies
So here are other possibilities for getting your geocoding done:
- SmartyStreets (Python) — or choose another
- Nominatim (OSM is OpenStreetMap)
- ggmap (if you use R and ggplot)
And if you are going to use a Google Map, then this code will be helpful to get your addresses geocoded for you.