How to use this calculator
- Enter or choose usable battery capacity.
- Enter or choose starting charge.
- Enter or choose target charge.
- Enter or choose charging efficiency.
- Enter or choose electricity price per kWh.
- The cost of this charge updates as you type. Use Copy result or Share to keep it.
Method
Battery kWh = Capacity × (Target% − Start%); Grid kWh = Battery kWh ÷ Efficiency; Cost = Grid kWh × Price + Fee; Range = Battery kWh ÷ Consumption × 100
- Efficiency
- share of grid energy stored in the battery
- Consumption
- battery energy used per 100 km
Worked example
- Battery energy = 60 × 60% = 36 kWh; grid energy = 36 ÷ 0.90 = 40 kWh.
- Cost = 40 × 0.30 = 12.00.
- Range added = 36 ÷ 18 × 100 = 200 km, so 12 ÷ 2 = 6.00 per 100 km.
Adding 36 kWh to a 60 kWh battery costs 12.00 at 0.30 per kWh, about 6.00 per 100 km.
What the result means
Compare the cost per 100 km with a petrol car’s fuel cost per 100 km, or with public charging prices, to decide where and when to charge.
Assumptions and limits
- One price per kWh for the whole session.
- Consumption is battery-side energy, as most trip computers report.
- Public chargers may also bill per minute or for idle time; add those as a session fee.
Questions
Why do I pay for more kWh than the battery receives?
Some energy is lost as heat in the charger, cables and battery, so the meter records more than is stored.
Is off-peak charging worth it?
If your tariff has a cheaper overnight rate, enter it here to see the difference; scheduling charging on a timer is usually free.