The practice of measuring electric vehicle (EV) charging efficiency by the time it takes to reach 80% state of charge (SOC) instead of 100% is based on several technical and practical reasons:
Battery Chemistry & Charging Curve
EV batteries follow a non-linear charging curve, where:
- 0% to 80%: Charging is fast because the battery can accept high power (constant current phase).
- 80% to 100%: The charging rate slows dramatically (constant voltage phase) to protect the battery from stress and overheating.
This means that:
- The first 80% is much quicker.
- The last 20% takes disproportionately longer (sometimes as long as the first 80%).
Let’s analyze it from the following aspects:
1. Power = Voltage * Current
2. Constant Voltage charging & Constant Current charging
3. Optimal charging curve. The on-board BMS system will communicate with the EV Charger based on information such as battery status/ temperature/ current capacity, and maintain the most suitable power for charging in the most suitable way.
4. How to charge an EV in the healthiest way?
Do not fully load, slow charging is the main method, and fast charging is supplemented. Please keep the battery at 20%~30% when parked for a long time, it is best to charge slowly every 3 months, and then discharge to 20%~30%.