Verification and diagnosis of a battery module

It is possible to carry out certain checks on a battery module without needing to open it. These checks allow for an assessment of its general condition and the detection of potential operational anomalies.

Measurement of open-circuit voltage

Using a multimeter connected to the + and – terminals of the battery, the open-circuit voltage (without any load connected) can be measured.

This value provides information on the overall state of charge of the battery.

Example:

For a 16S LiFePO₄ module, the nominal voltage is approximately 51.2 V, but it can vary:

Minimum voltage: 43.2 V (battery almost discharged)
Maximum voltage: 58.4 V (battery fully charged)

A measurement outside this range indicates a malfunction (damaged cell, BMS in protection, defective connection…).

Measurement of voltage under load

Another method is to measure the battery voltage when a consumer is connected (battery charging or discharging).

The voltage should remain stable and close to the open-circuit value.
A significant voltage drop when applying a load may indicate:
- a high internal resistance (ageing of one or more cells),
- a connection problem (poor contact or 'hot spot').

To confirm this latter case, a thermal camera can be used to identify overheating areas on the connections.

Diagnosis via communicating BMS

Some modern batteries are equipped with a communicating BMS, accessible via a dedicated application or interface.

This system allows real-time consultation of detailed information about the battery's condition, such as:

the SoC (State of Charge),
the internal temperature,
the number of cycles,
the fault codes or safety alerts (overvoltage, overheating, imbalance between cells, etc.).

This feature facilitates preventive diagnosis and maintenance without dismantling the module.

In summary

Type of check	Method	Information obtained	Signs of anomaly
Open-circuit voltage	Measurement at terminals with multimeter	Overall charge level	Value outside range 43.2–58.4 V
Voltage under load	Measurement with connected consumer	Voltage stability and internal resistance	Voltage collapse, overheating
Via communicating BMS	Mobile application or dedicated interface	SoC, T°, faults, cell balance	Error codes, unbalanced cell

*: The technical information presented in this article is provided for guidance only. It does not replace the official manuals of the manufacturers. Before any installation, handling or use, please consult the product documentation and follow the safety instructions. The site Torque.works cannot be held responsible for inappropriate use or incorrect interpretation of the information provided.