SoC (State of Charge)

With the growing development of electromobility and the increasingly widespread use of battery systems in vehicles and stationary energy storage, the parameter SoC (State of Charge) has become a commonly used term. SoC indicates the current charge level of a battery in percent, typically ranging from 0% (completely discharged) to 100% (fully charged).

Definition of SoC

State of Charge (SoC) describes the current amount of energy stored in the battery compared to its maximum usable capacity at any given time. The SoC value is given as a percentage. Unlike the SoH value, the SoC changes dynamically during charging and discharging.

For example, if a battery currently has a maximum usable capacity of 8 Ah and contains 4 Ah, then SoC = 50%. This means that half of the currently available capacity is in use.

In practice, there can be situations where two batteries show the same charge level (SoC), but their actual runtime differs. The reason lies in the difference in wear level – expressed as SoH (State of Health), which, unlike SoC, changes only gradually due to aging and repeated use. Thus, originally identical batteries can deliver different performance over time.

Specific example of SoC calculation:

• maximum usable battery capacity is 8 Ah
• battery is currently charged to 6 Ah
• calculation: 6 / 8 = 0.75 → SoC = 75%
• in other words: the battery is charged to 75% of its current maximum usable capacity

What is the difference between SoC and SoH:

• SoC (State of Charge) – indicates the current charge level of the battery, meaning how much energy is currently available. It is a short-term and variable parameter that constantly changes depending on usage and charging. Two batteries with the same specifications on the label but with different levels of wear may last different amounts of time at 100% charge (SoC = 100%). The reason is their different SoH, which affects the actual capacity of the battery.
  

• SoH (State of Health) – expresses the overall health condition of the battery, i.e., the degree of its wear and tear. This parameter changes slowly over time and indicates how close the battery is to its original (nominal) capacity. For example, a SoH of 80% means the battery can now hold only 80% of the energy it could when it was new. SoH is an important indicator of the battery’s lifespan and performance. More information about the SoH parameter can be found here.