ToolnozaHome charging cost formula
Energy stored (kWh) = usable battery capacity × (target charge − starting charge) ÷ 100. Grid energy = energy stored ÷ charging efficiency. Cost = grid energy × electricity price per kWh, plus any session fee.
Worked example: charging from 20% to 80%
For a 60 kWh usable battery, the 60 percentage-point increase stores 60 × 0.60 = 36 kWh. At 90% efficiency, the grid supplies about 36 ÷ 0.90 = 40 kWh. At $0.16 per kWh, estimated energy cost is $6.40 before fixed fees.
Check the tariff and efficiency
Use the price for the hours when charging occurs. Time-of-use plans can make overnight charging cheaper, but check the actual rate and any connection fees. Efficiency varies with the vehicle, charger, temperature and battery conditioning, so the estimate is not a guaranteed bill amount.
Frequently asked questions
Do I pay only for energy stored in the battery? Usually the meter records energy drawn from the grid, which can exceed stored energy. Does the estimate include public charging fees? Add them if applicable. Why does my result differ? Tariffs, efficiency and starting charge may differ from the assumptions.