Electric Vehicles
Wall-to-Battery Efficiency Calculator
Calculate wall-to-battery efficiency with an optional battery-energy adjustment. Do not use the adjustment to force an expected efficiency result.
Enter compatible measurements
Enter current information for Wall-to-Battery Efficiency and leave unrelated adjustments outside the form.
Uncertainty and omitted conditions
Control software, temperature, wiring loss, battery condition, and equipment limits can alter the measured electrical result — for ambient adjustment, the page specifically expects optional percentage adjustment to battery-energy estimate.
Because a different input set is required to apply a cold-weather loss and arrival reserve to a warm-weather EV range, use the Winter EV Range Loss for that calculation.
Working through the equation
Calculate wall-to-battery efficiency with an optional battery-energy adjustment — battery, charger, wall, and accessory measurements are not interchangeable.
Do not use the adjustment to force an expected efficiency result — that condition defines when adjusted charging efficiency is comparable with another result.
Wall energy is defined here as energy recorded by the charger or utility meter — keeping that definition intact requires you to identify whether the reading is taken at the source, charger, battery, or accessory.
For Battery energy gained, use the quantity described as increase in stored battery energy — in the vehicle record, identify whether the reading is taken at the source, charger, battery, or accessory.
Ambient adjustment: Optional percentage adjustment to battery-energy estimate — a compatible entry should keep the percentage basis explicit and do not mix a decimal fraction with a percent value.
In “efficiency = adjusted battery energy gained ÷ wall energy,” the equation links wall energy, battery energy gained, and ambient adjustment to adjusted charging efficiency.
No term beyond wall energy, battery energy gained, and ambient adjustment is introduced in “efficiency = adjusted battery energy gained ÷ wall energy.”
Sample arithmetic
The default values provide a calculation check: Wall energy = 32 kWh, Battery energy gained = 28.4 kWh, and Ambient adjustment = 0%.
The equation resolves that case as Adjusted charging efficiency = 88.8% and Adjusted battery gain = 28.40 kWh.
Use the EV Charger Breaker Size for the separate question of how to calculate the arithmetic relationship between EVSE current and a continuous-load breaker rating.
How the values should be read
Adjusted charging efficiency answers “Calculate wall-to-battery efficiency with an optional battery-energy adjustment.” The additional display, Adjusted battery gain, is a different view of the same entered measurements.
Measure both energy values over the same session boundary — when that condition changes, compare separate calculator runs instead of blending the inputs.
Because do not use the adjustment to force an expected efficiency result, a disagreement between adjusted charging efficiency and an outside reference should trigger a review of wall energy and ambient adjustment.
For the distinct decision to compare time-based public charging with an energy-based rate, preserve this answer and open the Per-Minute vs Per-kWh Charging.
Questions about the operating case
What measurement source fits Wall energy when it represents energy recorded by the charger or utility meter?
Because wall energy represents energy recorded by the charger or utility meter, use a source tied to the exact vehicle, component, and operating period described by the other fields.
How does the warning “Do not use the adjustment to force an expected efficiency result” affect Adjusted charging efficiency?
The condition “Do not use the adjustment to force an expected efficiency result” is not corrected automatically by the numeric inputs, so create a separate wall-to-battery efficiency case when it changes.
What assumption is expressed by “efficiency = adjusted battery energy gained ÷ wall energy”?
In “efficiency = adjusted battery energy gained ÷ wall energy,” wall energy and battery energy gained are treated as parts of one vehicle case.
How narrowly is Battery energy gained defined by “Increase in stored battery energy”?
The definition “Increase in stored battery energy” excludes a similarly named rating or a measurement taken at another reference point.