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Analysis by Marcus & Team

EG4 Battery: 100% SOC, No Discharge to Loads

EG4 battery showing 100% SOC but not discharging? Diagnose residential battery system issues. Check BMS, voltage, current limits, and safety measures.

Frequently Asked Questions

•What is the voltage reading at the battery terminals during discharge attempt?

If voltage drops significantly, battery issue. If no drop, inverter or communication issue.

•Are there any error messages displayed on the inverter or monitoring app?

Specific error codes can pinpoint the failing component or condition.

•Has the system recently experienced a power outage or other event that could have affected the BMS?

Power surges or brownouts can sometimes corrupt BMS settings.

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Marcus leads the technical research department at Storage Faults. Together with a team of systems analysts, he specializes in translating complex solar storage error codes into actionable diagnostic steps for the US market.

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Important Warnings:

Lithium-ion batteries store significant energy and pose a risk of thermal runaway, fire, and electric shock. High DC voltage is present. Always disconnect the DC disconnect switch before performing any work on the system. Only qualified electricians should perform electrical work on battery storage systems per NEC 706.10. Adhere to all applicable safety regulations and manufacturer guidelines.

Recommended Action:

1

Verify DC disconnect switch is closed and functioning correctly using a multimeter to measure voltage across the switch when closed (should be near 0V).
2

Check BMS parameters via the monitoring app or installer interface for discharge current limits and adjust if necessary.
3

Use a clamp meter to measure DC current at the battery terminals during an attempted discharge. No current indicates a problem with the BMS or DC disconnect.
4

Measure individual cell voltages using a multimeter to identify any significant cell imbalances. An imbalance greater than 0.2V may indicate a problem.
5

Use an IR thermometer to check for any hotspots on the battery module, which may indicate a failing cell. Refer to EG4 documentation for acceptable temperature ranges.
6

Check the communication status between the BMS and inverter. Refer to the manufacturer's documentation for specific troubleshooting steps. Often, this requires a qualified technician using specialized software.
7

Engage a qualified electrician to inspect and repair the system per NEC 706.15, especially concerning rapid shutdown compliance and safe disconnection procedures.

Technical Overview:

Residential battery storage systems typically consist of lithium-ion or LFP batteries, a Battery Management System (BMS), a DC-to-AC inverter, and grid-tie components. The BMS monitors cell voltages, temperature, and current to prevent overcharge/over-discharge and thermal runaway. The inverter converts DC battery power to AC for powering loads. Communication between the BMS and inverter is crucial for proper operation. The system must also comply with NEC rapid shutdown requirements.

Why This Happens:

BMS is incorrectly reporting SOC due to cell voltage imbalance or calibration error.
DC disconnect switch is open or faulty, preventing current flow from the battery.
Inverter is not properly communicating with the BMS, preventing discharge initiation.
Discharge current limit set to zero within the BMS parameters.
A faulty temperature sensor (NTC) is causing the BMS to limit discharge current as a safety measure.
Internal BMS fault causing it to shut down discharge.

Symptoms:

Battery system indicates 100% State of Charge (SOC) via monitoring app, but connected AC loads are not being powered by the battery when grid power is unavailable. DC bus voltage may be present, but no current flow detected during attempted discharge.

Preventative Care:

Perform regular visual inspections of battery modules for signs of damage or corrosion.
Monitor cell voltages and temperatures via the monitoring app and address any imbalances promptly.
Ensure firmware is up to date on both the BMS and inverter.
Conduct periodic capacity tests to assess the overall health of the battery. Refer to manufacturer documentation.
Follow manufacturer's recommendations for battery maintenance and cleaning.