5 Common BMS Failures and How to Prevent Them

The Battery Management System (BMS) is the brain of an electric vehicle (EV) or energy storage system, ensuring battery safety, performance, and longevity. However, like any critical component, BMS failures can lead to reduced efficiency, safety hazards, or even catastrophic battery damage.

In this article, we explore the five most common BMS failures and provide actionable solutions to prevent them.

1. Voltage Imbalance Between Cells
Problem:
Lithium-ion battery packs consist of multiple cells in series.

Over time, some cells may charge/discharge faster than others, leading to voltage imbalance.

If unchecked, weak cells can overcharge or over-discharge, reducing battery life.

Solution:
✔ Active Cell Balancing – Uses resistors or DC-DC converters to redistribute energy.
✔ Passive Balancing – Dissipates excess energy from high-voltage cells via resistors.
✔ Regular Diagnostics – Monitor cell voltages and correct imbalances early.

2. Overheating & Thermal Runaway
Problem:
Excessive heat from fast charging, high loads, or poor cooling can damage battery cells.

If temperatures exceed safe limits, thermal runaway (a chain reaction of overheating) can occur, leading to fires.

Solution:
✔ Temperature Sensors – Place multiple sensors across the battery pack.
✔ Cooling Systems – Use liquid cooling or forced air to maintain optimal temps.
✔ Current Limiting – Reduce charging speed if temperatures rise abnormally.

3. Communication Failures (CAN Bus Errors)
Problem:
The BMS communicates with the Vehicle Control Unit (VCU) and other systems via CAN bus.

Loose connections, EMI, or software bugs can disrupt communication, causing incorrect state-of-charge (SOC) readings or shutdowns.

Solution:
✔ Shielded Wiring – Prevent electromagnetic interference (EMI).
✔ Redundant Communication Lines – Ensure backup data pathways.
✔ Firmware Updates – Fix bugs and improve protocol stability.

4. Current Sensor Drift & Inaccuracy
Problem:
Hall-effect or shunt-based current sensors can lose calibration over time.

Incorrect current readings lead to wrong SOC estimates, risking overcharging or unexpected shutdowns.

Solution:
✔ Regular Calibration – Recalibrate sensors during maintenance.
✔ Dual-Sensor Redundancy – Cross-check readings for accuracy.
✔ High-Precision Sensors – Use high-quality sensors with minimal drift.

5. Software Glitches & Firmware Bugs
Problem:
BMS software controls critical functions like SOC estimation, fault detection, and safety protocols.

Bugs can cause false alarms, incorrect shutdowns, or failure to detect real faults.

Solution:
✔ Rigorous Testing – Simulate real-world conditions before deployment.
✔ Over-the-Air (OTA) Updates – Fix bugs without hardware recalls.
✔ Watchdog Timers – Automatically reset the BMS if it freezes.

How to Extend BMS Lifespan?
Preventive Maintenance – Regularly check connections, sensors, and cooling.
Quality Components – Use reliable BMS hardware from trusted suppliers.
Proper Installation – Follow manufacturer guidelines for wiring and placement.

Final Thoughts
A failing BMS can compromise safety, performance, and battery life. By understanding these common issues and implementing preventive measures, manufacturers and EV owners can ensure reliable operation and avoid costly failures.