EV charging cost with losses: home versus public charging
Separate battery energy from energy billed at the socket, then compare home and public tariff structures.
How it works
An EV battery does not receive every kWh drawn from the wall. For a simplified calculation, grid energy = battery energy ÷ charging efficiency. Multiply billed grid kWh by the tariff and add any session, parking or time-based fees. Actual efficiency varies with charger, temperature and power, while a public charger may bill per delivered kWh using a different boundary.
Use the inputs from your own situation and keep the units consistent. A calculator gives an arithmetic estimate under the assumptions you enter; compare it with real records before making a decision.
Worked example
If the battery needs 45 kWh and illustrative home charging efficiency is 90%, grid demand is 45 ÷ 0.9 = 50 kWh. At $0.20 per kWh, energy costs $10. A public session priced at $0.35 per delivered kWh plus a $2 fee would cost $17.75 for 45 kWh, before parking. Compare the billing definitions before treating $7.75 as a universal saving.
What to check
Some tariffs have peak periods, minimum fees, subscriptions, idle charges or tax. A battery percentage change is a rough energy proxy. Charging efficiency is an input assumption, not a fixed property of every charger. Check receipts and current tariffs rather than using old examples as live prices.
Practical next step
Enter the expected battery energy, realistic efficiency and actual tariff for each option. Add all fees and compare cost per usable kWh, then test a lower-efficiency case.
Related calculators and articles
ev trip cost, ev charge time, electricity. ev home charging cost year.
Save your assumptions and repeat the calculation if an input changes. The linked article explains a neighboring decision that this single formula does not settle.