Formula and meaning
The calculation compares energy measured at the wallbox or grid with energy actually stored in the battery.
η = E₍battery₎ / E₍grid₎ · E₍loss₎ = E₍grid₎ − E₍battery₎ · loss% = (1 − η) · 100
E-mobility · energy balance
EV Charging Loss Calculator
Calculate EV charging efficiency, lost energy and optional charging costs from measured energies.
EVAC/DC
02
Results
η = E_Akku / E_Netz
Set the inputs and run the calculation.
Context
67 kWh from the grid and 60 kWh stored in the battery give 89.55% efficiency, 7 kWh loss, and 10.45% loss.
Both measurements refer to the same charging event and system boundaries. Meter accuracy, standby consumption, and the selected measurement points affect the result.
Inputs and method
Charging losses from measurements
Compare grid and stored battery energy to calculate efficiency and losses.
Inputs
Grid/wallbox energy and battery energy must refer to the same session and boundaries.
Only identical measurement boundaries give a meaningful efficiency. Including wallbox standby, for example, makes loss look higher than in the battery charging path alone.
Calculation
η = Eᵦₐₜₜₑᵣᵧ/Egᵣᵢd; loss = Egᵣᵢd − Eᵦₐₜₜₑᵣᵧ.
Example
67 kWh grid and 60 kWh battery energy give 89.6% efficiency and 7 kWh loss.
Sources and limits: Energy balance; document measurement point, standby and meter accuracy.
Charging losses from measurements in detail
Compare grid and stored battery energy to calculate efficiency and losses.
What does this quantity describe?
Energy calculators balance quantities over time and separate useful energy, losses and grid import. This matters because power is instantaneous while energy is its time integral.
Formula and variables
η = Eᵦₐₜₜₑᵣᵧ/Egᵣᵢd; loss = Egᵣᵢd − Eᵦₐₜₜₑᵣᵧ.
Choose the inputs correctly
Grid/wallbox energy and battery energy must refer to the same session and boundaries. Only identical measurement boundaries give a meaningful efficiency. Including wallbox standby, for example, makes loss look higher than in the battery charging path alone.
How to use the calculator
Enter the energy measured at the grid/wallbox and the energy actually delivered to the battery for the same charging session. Optionally add the electricity price to quantify the cost of the losses.
Worked example
67 kWh grid and 60 kWh battery energy give 89.6% efficiency and 7 kWh loss.
Understand the result and units
Only identical measurement boundaries give a meaningful efficiency. Including wallbox standby, for example, makes loss look higher than in the battery charging path alone. An annual value describes a scenario, not a guarantee for every day. Efficiency, coincidence, temperature, driving profile and tariff assumptions can change practical results more than rounding.
Energy in kWh, efficiency and loss in percent, cost in euros.
Typical applications
Checking whether a charger or wallbox actually reaches its manufacturer-stated efficiency, or estimating the ongoing extra cost of charging losses across many sessions.
Assumptions, limits and common mistakes
Energy balance; document measurement point, standby and meter accuracy.
Common mistake: Don't compare energy values from different measurement points or charging sessions – grid and battery energy must refer to the same session and the same measurement boundary. Including wallbox standby power, for example, makes the loss look higher than in the battery charging path alone.
Frequently asked questions
Which values count as grid vs. battery energy?
Grid energy is the energy measured at the meter or wallbox; battery energy is the actually stored energy shown by the vehicle for the same charging session.
Why is charging loss never zero?
AC/DC conversion in the onboard charger, battery management, battery cooling/heating and cable resistance always turn some energy into heat; typical losses are around 5 to 15% depending on conditions.
Does outside temperature affect the measured loss?
Yes. In cold weather, battery preconditioning consumes extra energy, so measured loss is often noticeably higher than in summer.
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