How to use this calculator
- Enter or choose usable battery capacity.
- Enter or choose starting charge.
- Enter or choose target charge.
- Enter or choose charger power.
- Enter or choose car’s maximum charging rate.
- The charging time updates as you type. Use Copy result or Share to keep it.
Method
Energy = Capacity × (Target% − Start%); Power = min(Charger kW, Car limit kW) × Efficiency; Time = Energy ÷ Power
- Capacity
- usable battery capacity, kWh
- Efficiency
- share of grid energy stored in the battery
Worked example
- Energy = 60 × (80% − 20%) = 36 kWh.
- Power into the battery = 7.2 × 0.90 = 6.48 kW.
- Time = 36 ÷ 6.48 = 5.56 h ≈ 5 h 33 min; grid energy = 36 ÷ 0.9 = 40 kWh.
Charging a 60 kWh battery from 20% to 80% on a 7.2 kW charger takes about 5 hours 33 minutes.
What the result means
On AC home charging the estimate is usually close, because power stays near constant. At DC rapid chargers, power tapers as the battery fills, so the time above about 80% is longer than this constant-power estimate.
Assumptions and limits
- Charging power is constant for the whole session.
- The capacity entered is usable, not gross, capacity.
- Does not model DC taper curves, battery temperature or preconditioning.
Questions
Why does a 22 kW charger only give my car 11 kW?
On AC, the car’s onboard charger sets the limit. Enter that limit in the car field.
Why charge to 80% rather than 100%?
Charging slows near full, and many makers recommend a lower everyday limit to reduce battery wear. Check your car’s manual.