State of charge (SoC%) reading is inaccurate — how to calibrate

State of charge (SoC%) reading is inaccurate

The SoC percentage displayed on the BMS screen is a calculated estimate. Unlike the voltage reading which is always accurate, the SoC percentage can drift over time with repeated charge and discharge cycles. This article explains how to interpret your readings correctly and how to recalibrate when needed.

Always trust voltage over SoC%

The voltage reading on the BMS display is always accurate. Use the voltage-to-SoC reference table below to determine your actual charge level at any time, regardless of what the SoC percentage shows.

Voltage (VDC)	Actual SoC%
44.8	0%
46.1	10%
47.4	20%
48.8	30%
50.1	40%
51.4	50%
52.7	60%
54.0	70%
55.4	80%
56.7	90%
58.0	100%

Full SoC calibration procedure

Only perform this when you have access to shore power. The process takes several hours and should not be done off-grid.

1. Connect to shore power and charge until BMS voltage reaches 58VDC and the charging current drops to near zero (small negative or 0A value).
2. Disconnect shore power. Turn the PV Array DC Isolator to OFF. Turn the Main Switch Grid Supply to OFF. This removes all positive charge inputs.
3. Run 240V appliances to discharge the battery down to approximately 46.2VDC. The inverter will cut 240V output at this point.
4. Switch off 240V appliances and continue discharging using 12V appliances only such as lights and the fridge until the Battery Voltage Very Low warning appears and the system shuts down.
5. Restart the system and immediately connect to shore power. Charge fully until voltage reaches 58VDC and holds stable for approximately 1 hour.
6. The SoC% should now reflect 99 to 100%. The calibration is complete.

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