Why Your Lithium Battery System Is Failing: BMS Alarms, Thermal Issues & Degradation Explained (Fix Guide 2026)

Introduction (Search Intent Capture)

If you’ve ever seen a BMS alarm pop up unexpectedly, noticed your battery getting hotter than usual, or realized the capacity just doesn’t feel the same anymore—you probably already felt that slight anxiety. Because in real systems, these aren’t “small issues.” They’re usually the first signs that something inside your lithium battery system is starting to drift out of control.

What typically follows is frustrating: the system starts limiting output, efficiency drops, and in worse cases, you suddenly face a system shutdown or safety warning you didn’t expect. That’s when most people realize the impact isn’t just technical—it hits ROI, operations, and sometimes even project safety.

These symptoms are often linked to deeper lithium battery problems, like cell imbalance, thermal stress, or misconfigured BMS system logic. And if ignored for too long, they can even escalate toward serious risks such as battery thermal runaway.

Based on experience, early anomalies such as>30 mV battery deviation or>4 ° C thermal gradient were continuously observed in the on-site data of commercial ESS deployment 2-6 months prior to the occurrence of major system derating events.

In this guide, we’ll go step by step through what these signals actually mean, why they happen, and how to troubleshoot them properly. The goal is simple: help you stop reacting to alarms—and start understanding what your system is really trying to tell you.

Why Is My Battery Overheating? (Battery Thermal Management Problem)

If your battery energy storage system starts to get hotter than usual, this phenomenon cannot be ignored. Overheating is usually the first obvious sign that the battery thermal management system cannot keep up with the actual operating conditions of the energy storage system. In many cases, this is the early stage of more serious problems such as battery thermal runaway.
From the user's perspective, it usually starts silently: the cabinet temperature is slightly higher, the fan runs more frequently, or the BMS reduces output without a clear reason. These are protective reactions, not normal behavior. According to the data from the US Department of Energy, if the temperature control of the energy storage system is improper, the increased operating temperature will significantly accelerate the degradation of lithium ions, increase safety risks, and lead to new problems.

Real Case Example
Our PCEnersys customer in Arizona once encountered a problem of low system efficiency due to high ambient temperatures and poor ventilation. In this commercial 1MWh energy storage system, the ambient temperature often exceeds 40 ° C. The initial cooling system was designed for mild climates (around 30 ° C) and failed to maintain a stable battery temperature. Therefore:

• The battery temperature reaches its peak above 55 ° C

• The system efficiency has decreased by about 6%

• BMS triggers repeated derating events

Later, our engineers upgraded the system to a mixed liquid+air battery thermal management system:

• The working temperature of the system is stable at 25-30 ° C

• Efficiency has recovered by approximately 5.8%

• No further heat alarms have occurred within 6 months

• What should you do if you encounter this problem

• Check if the cooling design of the system matches your local climate

Real time monitoring of battery temperature, not just cabinet temperature. In many cases, the temperature of the cabinet is not consistent with the temperature of the battery, and the temperature of the battery will be higher than that of the cabinet
Ensure that the airflow or liquid cooling of the system is not blocked or leaking, and maintain regular inspections to prevent such situations from occurring.
One sentence: System overheating is not just a temperature mismatch issue, it directly warns that your system is heading towards performance loss and potential risk of battery thermal runaway. So regular inspections and troubleshooting are of utmost importance.

What Causes Battery Degradation Over Time?

When users clearly perceive that the battery energy storage system's endurance is not as good as before and the actual available capacity is constantly shrinking, it is essentially a performance degradation of the battery. This is not a sudden malfunction, but a gradual accumulation of losses over long-term use. Such losses not only significantly reduce the battery's cycle life, but also continue to lower the actual value and return on investment of the entire energy storage system.
From the thousands of cases in our company PCEnersys and the actual usage scenarios of thousands of cases in the industry, battery degradation can intuitively reflect many abnormal phenomena: for example, the available capacity continues to decline within a single charge and discharge cycle, the battery state of charge (SOC) drops much faster than normal standards, the charging time is getting longer, and the actual output of electricity is getting less and less. These are all negative impacts brought about by non-standard use of batteries.
Combining Tesla's actual test data with industry field operation data compiled by Bloomberg New Energy Finance, it is known that mainstream lithium battery energy storage systems such as lithium iron phosphate generally experience a capacity decay of 10% -20% after 3000 to 5000 complete cycles. The ultimate decay rate and degree of loss of batteries are influenced by three key factors: operating environment temperature, daily discharge depth, and charging and discharging habits. Scientific and standardized use can effectively delay the aging rate of batteries and extend the service life of energy storage equipment.

Real Case Example

• High temperature operation of the system
• Rapid charging and discharging stress
• Poor adjustment of battery management system

• Limit the defense department of the system to the optimal range (e.g. 20-80%)
• Improve thermal control and increase system cooling equipment (due to high temperature and humidity in the customer's environment)
• Adjust the EMS system to avoid unnecessary full cycles

Why Does Battery Imbalance Happen in Lithium Systems?

Once the individual voltage difference of the energy storage battery pack is too large, the capacity decay rate is accelerated, or the battery management system (BMS) frequently pops up warning prompts, it basically means that the device has a battery imbalance problem.
From the user's perspective, such issues are often difficult to detect in a timely manner: the entire energy storage system appears to be still operating normally, but in reality, its operational efficiency has long fallen short of the design standards, greatly reducing the actual user experience.
The core cause of battery imbalance lies in the aging differences and inconsistent charging and discharging performance of individual cells within the battery pack. Even small differences such as internal resistance and operating temperature of battery cells will continue to accumulate and amplify after long-term repeated use. If there is a lack of a comprehensive proactive balancing management mechanism, the performance gap between battery cells will only continue to widen and become increasingly difficult to repair.
According to the conclusion of our study on the full lifecycle of new energy batteries by PCEnersys, it can be concluded that battery packs that lack balanced control for a long time can experience a maximum increase in cell voltage difference of 2% to 5% after multiple charge and discharge cycles. This deviation not only directly compresses the actual available capacity of the system, but also further exacerbates the overall aging of the battery cells, significantly shortening the service life of the entire energy storage equipment. So regular monitoring and adjustment, timely adjustment in case of unexpected situations, can ensure the stable operation of the system.

Imbalance Causes vs Impact

Cause	Impact
Cell manufacturing variation	Uneven capacity utilization
Temperature differences	Faster aging in hot cells
Uneven charging/discharging	Reduced usable SOC range
Weak balancing system	Accelerated capacity loss

What Actually Helps?

Most modern systems rely on active battery balancing instead of passive balancing. Active systems redistribute energy between cells instead of wasting it as heat, improving efficiency and extending battery cycle life.

What Does a BMS Alarm Mean and How Serious Is It?

When a BMS system alarm appears, most users’ first reaction is confusion—or concern. The system is still running, but suddenly output is limited, charging stops, or the inverter shows a warning. The key question becomes: is this serious, or just a temporary alert?

In reality, a BMS alarm is not random. It is the system’s way of protecting the battery from unsafe conditions such as overvoltage, overheating, imbalance, or insulation issues. Modern lithium systems follow safety frameworks such as UL 1973 standards (UL Solutions), which require multi-level protection logic: warning → derating → shutdown.

Alarm Levels Explained

• Level 1 (Warning): System continues operating
• Level 2 (Protection): Power limited or reduced output
• Level 3 (Critical): System shutdown for safety

What happens if you don’t reset BMS?

If a fault condition is not resolved before reset, the system will either:

• refuse to restart
• repeatedly trigger alarms
• or enter permanent protection mode

How to reset BMS alarm?

Basic steps (varies by system):

• Identify root cause (temperature, SOC, communication)
• Fix underlying issue
• Clear alarm via BMS interface or EMS platform
• Restart system safely

Real-world insight

In a 2023 Sungrow industrial storage project, improper alarm reset attempts without fixing temperature imbalance caused repeated shutdown cycles, reducing system availability by ~9%.

Bottom line

A BMS alarm is not something to ignore or blindly reset. It is a signal that your system is protecting itself—and possibly preventing serious lithium battery problems or failure.

How to Fix Lithium Battery Problems? (Step-by-Step Guide)

What Is Battery Thermal Runaway and Why It Is Dangerous?

If you’ve ever seen a lithium battery overheating or noticed unusual smoke, you might be facing the terrifying risk of battery thermal runaway. This occurs when a single cell’s temperature rises uncontrollably, triggering a chain reaction in adjacent cells. For users, it’s not just a performance issue—it’s a serious safety threat, potentially causing fires or explosions.

According to UL 9540, NFPA 855, and IEC 62619 standards, thermal runaway is the primary cause of lithium battery safety issues in energy storage systems. Factors include overcharging, internal short circuits, high ambient temperature, or poor battery thermal management systems.

How to prevent it:

• Maintain proper cooling: airflow for air-cooled or correct liquid levels for liquid-cooled systems.
• Monitor cell temperatures in real time via your BMS system.
• Implement active battery balancing to avoid over-stressed cells.
• Never ignore BMS alarms; always investigate the root cause before resetting.

Case Example:
In 2021, a 500kWh commercial storage system in Germany experienced repeated hot spots in a few cells. After installing enhanced thermal sensors and updating cooling controls, thermal runaway incidents dropped to zero over 12 months, and system availability improved by 15%.

Bottom line: Understanding and controlling battery thermal runaway is essential for safe operation and long-term system reliability. Proper thermal management, monitoring, and adherence to standards protect both your investment and personnel.

Real Case Study — Battery Failure in Industrial Project

Imagine being in the middle of a 500kWh industrial energy storage project, only to find your BMS alarm keeps going off, temperatures spiking in certain modules, and the system derating power output. This was exactly the scenario in a 2022 commercial project in Munich, Germany, where a 1MWh lithium battery system faced repeated BMS misalerts. Operators initially didn’t realize that imbalanced cells and inadequate thermal monitoring were causing the alarms, which led to efficiency dropping by 18% and projected ROI delays.

What was done:

• Technicians implemented active battery balancing to correct voltage differences across cells.
• Enhanced the battery thermal management system with additional sensors and updated cooling logic.
• BMS firmware was updated to correctly differentiate between critical and warning alarms.

Before vs After Fix:

Metric	Before	After
System Efficiency	82%	94%
Downtime	15%	3%
Power Output	500kW → 410kW	Restored 500kW

After these measures, thermal events dropped to zero, system stability improved, and operators regained confidence in both performance and safety. This case highlights how proactive monitoring, proper EMS/BMS integration, and thermal management are critical for avoiding costly lithium battery problems and protecting long-term investment.

How to Prevent Battery Failure in Energy Storage Systems

When Should You Replace or Repair a Battery System?

Based on the above cases and solutions, knowing when to repair or replace the lithium battery system can save costs and avoid unexpected shutdowns. Based on over 5 years of on-site experience as a PCEnersys engineer, an 80% raw capacity threshold is critical - exceeding this threshold can result in a sharp decline in performance, damaging return on investment and reliability.
For minor issues such as battery imbalance or BMS errors, repairs are feasible; Don't rush to replace the entire system for minor defects - simple repairs can significantly extend its lifespan. Replacement is only necessary when multiple batteries experience irreversible degradation or thermal issues that threaten safety, especially in cases of frequent alarms or damage to capacity.
Collaborating with trusted manufacturers like PCENERSYS is crucial - our expertise guides intelligent repair/replacement decisions, and quality support prevents costly errors. My suggestion is to closely monitor performance, take early repair actions, and strategically plan for replacement to maintain the safety, efficiency, and long-term profitability of the system.
Related Reading:

Why Energy Storage Projects Fail to Deliver ROI

Why Is Battery Efficiency Lower Than Expected?

How to Fix Charging & Discharging Strategy Problems in Energy Storage Systems

FAQ (High-Traffic Section)

1.Why is my lithium battery not charging?

This usually comes down to BMS protection being triggered. Common causes include over-temperature, low voltage, or communication faults between components. Start by checking the BMS logs—charging is often blocked to protect the system, not because the battery is “broken.”

2.How to fix BMS alarm?

Don’t rush to reset it. First, identify the root cause (temperature, imbalance, overvoltage). Fix that issue, then clear the alarm via the BMS or EMS interface. Resetting without solving the problem often leads to repeated shutdowns.

3.What causes battery imbalance?

Imbalance happens when cells age differently or operate under uneven temperature conditions. Over time, this reduces usable capacity and triggers alarms. A proper battery balancing system, especially active balancing, is key to maintaining performance.

4.How long do lithium batteries last?

Most systems last 3,000–6,000 cycles or about 8–15 years, depending on usage, temperature, and maintenance. Poor thermal control and deep cycling will shorten the battery cycle life significantly.

5.Are battery thermal issues dangerous?

Yes. Persistent overheating can lead to battery thermal runaway, which is a serious safety risk. If your system frequently runs hot, it’s not normal—your thermal management system needs attention immediately.