State of charge (SoC)

State of charge

The battery's current fill level as a percentage, like a fuel gauge. Charging speed and everyday charging habits are described in SoC terms.

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State of charge is how full the battery is, expressed as a percentage: the EV world's fuel gauge. The reason it earns its own vocabulary is that so much EV behavior is described in SoC terms rather than in kWh.

Charging speed depends on it. The Australian Government lists the battery's state of charge, for example 30%, among the factors that set charging speed, and says the highest rates are usually between 20% and 80%, with the final 20% generally slower. That is the charging curve, and why quoted times use a window such as 10–80%.

Daily habits reference it too. The Australian Government says some battery chemistries and battery management systems prefer to operate between 20% and 80% state of charge, while others recommend charging to 100% weekly, so follow the owner's manual and check whether your car lets you set a charge limit.

The US Department of Energy notes that the onboard charger monitors battery characteristics, including state of charge, while charging.

  1. Australian Government, Electric vehicle charging equipment
    Australian Government Accessed
  2. Australian Government, Electric vehicle maintenance and servicing
    Australian Government Accessed
  3. US DOE Alternative Fuels Data Center, How Do All-Electric Cars Work?
    US Department of Energy Accessed

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