Estimate public fast charging cost.
Public rapid charging is priced per kilowatt-hour but rarely billed that way alone. A connection fee and, increasingly, an idle fee for occupying the bay after the session completes are added on top, and both fall disproportionately on small top-ups. Dividing the all-in total by the energy actually delivered gives the effective price per kilowatt-hour, which is the only figure that lets you compare a network with a low headline rate and a high connection fee against one without.
Session total
Total = kWh x price per kWh + session fee + idle minutes x idle rate
Effective rate
Effective price per kWh = total cost / kWh delivered
The hardware, grid connection and demand charges for a 150 kW charger are an order of magnitude above a home wallbox, and networks recover that in the per-kWh rate. Expect roughly three to four times the home tariff.
Set a charge limit and a phone alert, and treat the bay as a fuel pump rather than a parking space. Fees typically start five to ten minutes after the session completes and run at a rate that quickly exceeds the energy cost.