Understanding your result
Battery energy is the amount stored. Charger energy is higher when efficiency is below 100%, and that charger energy drives the energy-based bill. Time uses the average input power you specify for the whole session.
To compare charging energy with a solar production estimate, use the Solar Energy Calculator for the same period.
The formula
A state-of-charge change describes a fraction of usable battery capacity. Dividing by wall-to-battery efficiency adds conversion and charging losses. Since power is entered at the charger side, time must use charger energy rather than battery energy.
Worked example
A 60 kWh usable battery moving from 20% to 80% stores 36 kWh. At 90% efficiency it draws 40 kWh. With an average input of 7.2 kW, that takes about 5.556 hours and costs 8 at a tariff of 0.20 per kWh.
How to use this calculator
- Use usable battery capacity rather than gross pack capacity.
- Enter current and desired charge percentages.
- Estimate session-average input power, efficiency, and the energy tariff.
Rated power is not a charging curve
Vehicle limits, charger limits, battery temperature, and charge level affect power. Fast charging often slows as the battery fills. Entering a charger’s peak rating as the average can therefore underestimate duration. The target table deliberately holds your average-power assumption constant; it is not a vehicle-specific prediction of tapering.
Energy tariffs and other session fees
The cost result covers energy priced per kWh at the charger. Per-minute billing, idle fees, subscriptions, parking, and session-start fees need separate treatment. If the provider’s meter or quoted efficiency uses a different measurement point, align that basis before comparing the estimate with an actual invoice.
Assumptions & limitations
What this calculation assumes
- Usable capacity, average input power, and efficiency remain fixed for the estimate.
What to keep in mind
- No live vehicle charging curve, battery-temperature model, or provider pricing feed.
Common questions
Why does charging draw more than the battery gains?
Some energy is lost during conversion and battery charging, or used by vehicle systems. The efficiency field represents the combined effect assumed here.
Can the target equal the starting charge?
Yes. With no requested change, this model returns zero additional energy, time, and energy cost.