Plain-language answer: Battery state of charge estimates the remaining usable charge as a percentage of the battery’s present full capacity.
Why it matters
Voltage alone may mislead under load, after charging, or with lithium chemistries; temperature, aging, current history, and calibration affect the estimate.
Use it correctly
Use a chemistry-appropriate monitor, account for current over time, let voltage settle when using open-circuit checks, and verify usable capacity periodically.
The common mistake
Treating a momentary terminal voltage as an exact fuel gauge.
Decision boundary
Current regulation, program rules, manufacturer limits, exact station configuration, and live observations control. Recheck changing rules, solar conditions, and operating status before acting.
