State of Charge (SoC)

State of Charge (SoC) is a measurement that indicates how full a battery is at any given moment, expressed as a percentage from 0% (completely empty) to 100% (fully charged). It is the battery equivalent of a fuel gauge.

SoC is one of the most important metrics displayed on your solar battery’s monitoring app or portal. Knowing your battery’s SoC helps you understand how much backup energy is available and how your battery is cycling throughout the day. Most home battery systems are programmed to maintain a minimum SoC reserve (typically 10–20%) to protect the battery from deep discharge, which can reduce its lifespan. For example, if your battery has a 20% reserve, it will stop discharging at 20% SoC even though it technically has energy remaining. During normal operation, your battery might charge to 100% from solar during the day, discharge to 20–30% overnight, and recharge the next morning. Monitoring SoC patterns over time can help you determine if your battery is sized appropriately for your household’s needs.