By EV Charge Cost Editorial Team. Published September 28, 2026, updated October 26, 2026.
Where the energy goes
Between the outlet and the battery, electricity passes through several stages, and each one turns a little of it into heat:
- The onboard charger. On Level 1 and Level 2, the car converts AC from the grid into DC for the battery. That conversion is the largest single loss for most home charging.
- Wiring and cables. Resistance in the circuit, the charging cable and the car's high-voltage wiring produces heat. Losses rise with current.
- The battery itself. Cells have internal resistance, so pushing energy in warms them.
- Keeping the car awake. Control computers, pumps and fans run during the whole session. On slow charging the session is long, so this fixed overhead becomes a larger share of the energy.
- Battery heating or cooling. In cold or hot weather the car may spend energy conditioning the pack before and during charging.
Why the EPA rating already covers it
EPA tests measure the energy drawn from the wall to recharge the car after a test drive. So kWh per 100 miles is a wall-to-wheels figure. When our calculators multiply it by your price, the result is the cost of the electricity actually billed, losses included. Adding another loss factor on top would double-count.
Why your dashboard may disagree
Many cars' trip computers report energy drawn from the battery, not from the wall. That number is lower than what your meter records. Suppose, as an illustration, your trip computer shows 29.5 kWh/100 mi. The wall energy depends on how much was lost during charging:
| Illustrative loss | Wall kWh per 100 mi | Cost per 100 mi | Cost per year (13,500 mi) |
|---|---|---|---|
| 5% | 31.1 | $5.64 | $761.29 |
| 10% | 32.8 | $5.95 | $803.58 |
| 15% | 34.7 | $6.30 | $850.85 |
| 20% | 36.9 | $6.70 | $904.03 |
The math: wall energy = battery energy ÷ (1 − loss share). Each step of 5 points in losses moves the yearly bill by a few dollars to a few tens of dollars at average prices. It matters, but it is far smaller than the gap between states, where the same car costs $4.26 per 100 miles in Nevada and $15.81 in Hawaii.
What makes losses bigger or smaller
Charging power
Level 1 charging on a 120 V outlet typically loses a larger share than Level 2, mainly because the car stays awake for many more hours to deliver the same energy. See Level 1 vs Level 2 charging.
Temperature
A cold battery accepts charge less readily and may need heating first. Charging right after a drive, while the pack is warm, or scheduling charging to finish near departure can help in winter.
DC fast charging
With DC fast charging, the AC-to-DC conversion happens inside the station, bypassing the car's onboard charger. You pay for whatever the station meters, which includes some losses of its own depending on where it measures. High current also heats the battery, which may need active cooling.
How to measure your own losses
- Note the kWh your charger or utility meter records for a session. Many smart chargers show this in their app.
- Note the kWh the car says it added, or estimate it from the percentage gained times usable capacity.
- Loss share = 1 − (car kWh ÷ wall kWh).
For example, if the meter records 40 kWh and the car reports 36 kWh added, the loss share is 1 − 36 ÷ 40, or 10%. At 18.16¢/kWh, the 4 lost kWh cost $0.73, which is money spent on heat rather than miles.
Treat a single session with caution; averages over several weeks are more reliable. For the full picture of what one charge costs, see usable vs gross battery capacity, and for your yearly total use the charging cost calculator.