Formulas
- Energy added = battery × (end % − start %)
- Energy from the grid = energy added ÷ charging efficiency
- Time = energy from the grid ÷ charger power
Example
Charging a 75 kWh battery from 20% to 80% on an 11.5 kW Level 2 charger takes about 4 h 21 min and costs $8.00 at $0.16/kWh. That adds about 161 miles, saving $10.75 compared with a 30 mpg car at $3.50 a gallon.
Charger levels
- Level 1 (120 V outlet): about 1.4 kW, a few miles per hour.
- Level 2 (240 V): 7 to 11.5 kW, a full night covers most needs.
- DC fast charging: 50 to 350 kW, but slows down above 80%.
Frequently asked questions
Why is the real time longer?
Above about 80% the car slows charging to protect the battery, and cold weather slows it too.
Does charging at home really cost less?
Usually yes, especially at night rates. Public fast chargers often cost two to four times more per kWh.
See also
Results are estimates for information only and are not financial, legal or medical advice. Rates, taxes and fees vary — confirm with a professional or your lender.