State of Charge

State of charge (SoC) is how full a battery is, shown as a percentage of its capacity. 0% is empty and 100% is full.

Every charging calculation starts with the gap between the starting and ending state of charge. Taking a 75 kWh EV battery from 20% to 80% adds 60% of 75 kWh, or 45 kWh. A 100 Ah battery charged from 50% to full needs 50 Ah. Set both percentages in the EV charging time calculator or the battery charging time calculator.

Charging speed changes with state of charge. Lithium-ion fills quickly to about 70%, then slows as it nears full. The FAQ on why EV charging slows down at 80% explains why.