PRACTICAL GUIDES · Finance and work
What does a charge cost? Work from battery level to billed energy
A battery percentage is not a direct measurement of the energy you pay for. A useful estimate separates stored energy, input energy and the service’s billing basis.
1. Gather consistent inputs
Use a usable battery capacity that matches the starting and ending percentages. Do not automatically replace it with advertised nominal capacity when those values differ.
Read the rate applicable to your electricity agreement or charging session. This guide uses hypothetical prices, not current prices for a particular utility or charging network.
2. Calculate the energy to add
The difference between ending and starting charge levels gives the fraction of usable capacity to replenish. Going from 20% to 80% adds 60% of capacity, rather than 80%.
That amount reaches the battery. Estimating input energy requires a definition of losses: our calculator treats the loss percentage as a share of input energy.
EV charging cost calculator3. Enter the rate and fixed fee
In Charging cost, set capacity, charge levels, loss percentage, price per kWh, fixed fee and currency. Add the fixed fee once for the scenario being modeled.
If the service already bills measured energy at a defined point, avoid adding losses that are already included. Per-minute charges, parking and subscription costs require separate consideration.
TRY THIS STEP
EV charging cost calculator
Use the full calculator here: load the example values, then change one input at a time and compare the result with the steps in this guide.
A reproducible example
The example uses 60 kWh, 20% to 80%, 10% losses, 0.30 EUR/kWh and a fixed fee of 1 EUR. Expect 36 kWh to the battery, 40 kWh from the grid and 13 EUR. Change one variable at a time; this is a hypothetical tariff.
Result
Your result will appear here.
4. Complete example: 20% to 80%
Assume 60 kWh of usable capacity, a hypothetical loss of 10% of input energy, a rate of $0.25/kWh and a $1 fixed fee. Calculate energy before applying the price.
A hypothetical $11 session
- Starting point
- 60 kWh; 20% → 80%; 10% loss; $0.25/kWh; $1 fixed fee
- Result
- 36 kWh stored, 40 kWh input, estimated cost $11
Calculation steps
Calculate the energy that must reach the battery.
Divide by the fraction of input energy that reaches it.
Apply the rate to input kWh and add the fixed fee.
Reverse check: 90% of 40 kWh is 36 kWh. The cost applies to these stated assumptions and charges, not to every charging service.
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40 kWh input
Energy entering the modeled process.
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36 kWh stored
90% of input energy.
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4 kWh lost
The remaining 10% under this assumption.
5. Avoid counting losses twice
At a loss of 10% of input energy, 90% reaches the battery. Adding 36 kWh therefore requires 40 kWh of input. Multiplying 36 by 1.10 gives 39.6, which represents a different loss definition.
Actual losses vary with the vehicle, charging power and conditions. The example’s 10% is not a universal allowance. Also distinguish kW, a unit of power, from kWh, a unit of energy.
| Quantity | Meaning |
|---|---|
| kWh | Energy |
| kW | Power |
| $/kWh | The example rate, not a universal price |
6. Compare with an actual charging session
After charging, compare levels, metered kWh and billed items. If totals differ, check the billing basis and additional charges before revisiting capacity and assumed losses.
The charging-time calculator uses an assumed average power. It does not model the entire charging curve, so its estimate is not a promise of the next session’s duration.
These are example inputs, rather than measurements of a real case. Results use the full tool’s calculation engine. Compare them with the worked steps in this guide, then tick the checks after reviewing.
Sources and method
Frequently asked questions
Why not just multiply capacity by the rate?
That describes only a simplified case. A partial session requires the change in battery level, and input energy and fees may affect cost.
Can I enter zero loss?
Yes, for a scenario without additional losses. That choice must match the energy measurement and billing point you are using.