EV charging losses explained: what you actually pay for
A charger can draw more electricity than the amount stored in your EV battery. That difference is important when you compare charging prices. This guide shows the exact assumption used by Voltavena, with a worked example you can reproduce.
What are EV charging losses?
Charging losses are the difference between electricity drawn from the supply and energy that reaches the battery. Voltavena defines its loss percentage as a share of electricity drawn from the grid, not as a percentage added on top of the battery energy. This keeps the energy balance clear.
Why does the electricity meter show more energy?
Some energy is used during AC/DC conversion, in cables and electronics, and by the battery temperature-management system. Auxiliary systems may also draw power while the car is connected. Conditions and equipment affect the result, so a fixed percentage is only an assumption, not a measured fact about your vehicle.
Worked example: adding 20 kWh to the battery
Assume 20 kWh is stored in the battery, losses equal 10% of grid energy and the example electricity price below applies. There is no separate session fee.
Added to the battery
20 kWh
Bought from the grid
22.22 kWh
Energy lost along the way
2.22 kWh
Estimated charging cost
€6.67
The sample electricity price is an illustrative input for the selected country, not a live tariff. A different car, charger, charging temperature or session fee changes the result.
Why divide by 1 minus the loss percentage?
If 10% of energy purchased from the grid is lost, 90% reaches the battery. So battery energy = grid energy × 0.90. Rearranging gives grid energy = battery energy ÷ 0.90. Simply multiplying 20 kWh by 1.10 underestimates the energy purchased under this definition.
20 kWh ÷ (1 − 0.10) = 22.22 kWh
How to estimate losses from your own session
Compare kWh billed by the charger or electricity meter with a reliable measure of energy actually added to the battery for the same session. Loss share = (meter kWh − battery kWh) ÷ meter kWh × 100%. Battery state-of-charge percentages alone do not provide an exact battery-energy measurement. If you lack reliable measurements, treat your chosen loss percentage as a scenario.
Common questions
Is 10% a typical fixed charging loss?
No. Here it is an arithmetic example, not a claimed average. Charging power, equipment, temperature and auxiliary loads can change actual losses.
Are charging losses the same as battery degradation?
No. Charging losses describe energy not stored during a particular charging session. Battery degradation is a change in battery capacity over time.
Do charging subscriptions and session fees count as losses?
No. They are monetary charges rather than lost electricity. Voltavena adds any session fee separately in the charging-cost calculator.
Calculate your own charging cost
Read our calculation methodologyBackground sources
The US Department of Energy describes charging equipment and efficiency losses. These sources support the physical principles, not the example electricity prices or a universal loss rate.