How it is calculated
- Battery energy added = usable capacity × (target charge − starting charge).
- Estimated wall energy = battery energy added ÷ (1 − loss allowance).
- Estimated session total = wall energy × price per kWh + session fee.
10 · Session cost
Estimate the cost of one charging session
Estimate a single charging bill by separating energy stored in the battery from energy billed at the plug. Add a fixed session fee and choose a loss allowance that suits the charging setup.
Your inputs
Get your result
Use your own figures or load the worked example below. All calculations stay in this browser.
Actual billing may use metered wall energy, time, idle fees, taxes, or a different rounding rule.
How to use this tool
- Set usable battery capacity and starting and target charge percentages.
- Enter the billed price per kWh, loss allowance and any fixed session fee.
- Calculate the stored energy, wall energy and itemized session total.
Worked example
A 25% to 80% paid charging session
- Usable battery
- 75 kWh
- Starting charge
- 25 %
- Target charge
- 80 %
- Price per kWh
- 0.35 per kWh
- Charging loss allowance
- 10 %
- Session fee
- 0
- Currency display
- US dollar ($)
Expected result 41.3 kWh stored · 45.8 kWh billed · $16.04 total
75 × 55% = 41.25 kWh stored. At 10% loss, 41.25 ÷ 0.90 = 45.833 kWh is billed. Multiplying by $0.35 gives $16.0417, rounded to $16.04.
Transparent estimates
How to read this result
The loss is a share of wall energy, so a 10% loss means dividing by 0.90. Time charges, idle fees and taxes need to be added separately if they are not covered by the fixed fee.
Assumptions
- The entered loss percentage represents the share of wall energy not stored in the battery.
What this estimate cannot tell you
- Provider taxes, time-based fees, idle charges, and minimum billing increments are not included unless entered as the session fee.