How the calculation works
Grid energy = battery capacity × state-of-charge change ÷ charging efficiency; time = battery energy added ÷ effective charging power.
- Convert the difference between target and starting charge into a battery fraction.
- Multiply usable battery capacity by that fraction to find energy stored.
- Divide by charging efficiency to estimate grid energy and multiply by the electricity tariff.
- Divide battery energy by effective charging power for ideal time; scale full-charge range by the same charge fraction.
Worked example
A 60 kWh battery charged from 20% to 80% adds 36 kWh to the battery. At 90% efficiency it draws 40 kWh; at AUD 0.30/kWh the session costs AUD 12.00 and takes an ideal 5 hours at 7.2 kW.
Assumptions
- Battery capacity is usable capacity, not gross pack capacity.
- The entered charger power is the effective power reaching the battery before tapering.
- Range scales linearly with state of charge for this planning estimate.
Limitations and responsible use
- DC fast charging commonly tapers, particularly at high state of charge.
- Temperature, battery conditioning, auxiliary loads and vehicle limits can increase time and energy.
- Tariffs may include time-of-use bands, session fees or demand charges not represented by one rate.
Sources and data checks
Source links were reviewed on 4 September 2026. Recheck time-sensitive rates and rules before relying on the result.