Why Do NMC Batteries Swell and How Can You Prevent It?

Are your products failing because of swollen batteries? This problem can lead to angry customers, damaged brand reputation, and expensive product recalls, leaving you feeling frustrated and out of control.

The main reason NMC batteries¹ swell is due to gas buildup² inside the cell. This happens when the internal chemistry breaks down, a process often triggered by overcharging, exposure to high temperatures³, physical damage, or simply poor manufacturing quality. Preventing swelling starts with understanding these triggers.

Swelling is a clear sign that something is seriously wrong with a battery. It's not just a cosmetic issue; it's a safety hazard and a major business risk. In my years of experience, I've seen this problem sink product lines and ruin company reputations. With new regulations coming, especially in Europe, a swollen battery is no longer a simple warranty claim. It can trigger investigations and even force you to recall entire product batches. This is a risk you can't afford to take. So, let's dive into what really causes this and what you can do to protect your business and your customers.

What is the main cause of battery swelling?

You've seen a battery puff up like a pillow, but you're not sure why. This uncertainty makes it hard to fix the problem, leaving you wondering if it's your fault or the manufacturer's.

The primary cause of battery swelling is the generation of gas from electrolyte decomposition. This chemical reaction is accelerated by four main factors: overcharging, high temperatures, deep discharging, and internal short circuits. Poor manufacturing quality is the biggest underlying reason these factors lead to catastrophic failure.

Let's break down these causes. Inside every NMC battery is a liquid called an electrolyte. When everything works correctly, this liquid helps energy flow smoothly. But when the battery is stressed, the electrolyte starts to break down and release gas. This gas has nowhere to go, so it pushes against the battery's casing, causing it to swell.

I've seen many clients come to us after experiencing this exact issue. One of them, a developer of portable medical devices, was promised "A-grade" cells by another supplier. For a few months, everything seemed fine. Then, the customer complaints started rolling in. The batteries in their devices were swelling. After a quick investigation, we found the root of the problem. The so-called "A-grade" cells were inconsistent. Some had tiny impurities from the factory, while others had poorly aligned internal components. These tiny defects create hotspots and weak points inside the battery.

Here’s a simple breakdown of the main triggers:

A quality Battery Management System (BMS)⁴ can protect against overcharging and deep discharging, but it can't fix a poorly made battery. That’s why the real problem often starts at the factory.

How to stop batteries from swelling?

A swollen battery is a ticking time bomb for your product's reliability. You feel helpless as your inventory becomes a potential hazard, threatening your business and your customers' safety. You need a way to stop this.

While you can't reverse swelling in a battery that's already puffed up, you can prevent it from happening in the first place. The key is to use a high-quality Battery Management System (BMS), operate the battery within its specified temperature range, and, most importantly, source your batteries from a truly reliable manufacturer.

Prevention is the only real solution here. Once a battery swells, it is permanently damaged and must be safely disposed of. Trying to use it is a serious fire risk. So, all our efforts must focus on stopping the swelling before it starts.

The first line of defense is a well-designed BMS. Think of it as the battery's brain. It constantly monitors voltage, current, and temperature. If it detects a dangerous condition, like the start of an overcharge, it immediately cuts off the circuit. A cheap or poorly calibrated BMS is almost as bad as having none at all.

Second, you must control the environment. Never leave battery-powered devices in a hot car or in direct sunlight for long periods. Heat is the enemy of battery health. We design our batteries with specific operating temperature ranges, and staying within them is crucial.

But the most important step happens long before the battery ever reaches you. It happens during sourcing. I can't tell you how many times I've heard suppliers in China talk about "A-grade cells." The hard truth is that there is no official, national standard for what "A-grade" means. It's just a marketing term. A supplier can call any cell A-grade. Many factories will use cheaper, recycled, or B-grade cells to cut costs, and you won't know the difference until a few months later when they start swelling. At Litop, we have a strict Incoming Quality Control (IQC) process for every cell we purchase. We can provide full traceability reports because we know that real quality isn't just a promise; it's a process you can verify.

How to protect an NMC battery?

You've invested in what you believe are good NMC batteries. But now you're constantly worried that they will degrade, fail, or worse, become a safety issue for your customers. This anxiety is draining.

To properly protect an NMC battery, you need a multi-layered approach. Use a robust BMS for electrical safety, store it in a cool, dry place at a 40-60% charge level, and ensure its physical casing prevents punctures or impacts. Above all, use the manufacturer-specified charger.

Protecting your battery is about creating a safe bubble around it—physically, electrically, and environmentally. Let's look at each layer.

First, physical protection. This is more than just avoiding obvious drops. For many of our clients in the wearable and medical fields, space is extremely tight. A battery that doesn't fit perfectly can move or vibrate, putting stress on its internal components and connections. This is why we specialize in custom-shaped and curved batteries. We design them to fit the device's cavity precisely, which immobilizes the battery and significantly reduces the risk of physical damage over the product's lifespan.

Second, electrical protection. We've talked about the BMS, but the charger is just as important. Using a cheap, uncertified charger is like feeding your high-performance battery a diet of junk food. These chargers often provide unstable voltage and current, which slowly damages the battery's chemistry with every charge. It creates micro-damage that eventually leads to bigger problems like swelling. Always use the charger specified by the battery manufacturer.

Finally, storage and environmental protection. If you need to store batteries for an extended period, don't leave them fully charged or fully empty. The ideal state of charge for storage is around 40-60%. This level puts the least amount of stress on the battery's internal chemistry. And always store them in a cool, dry place.

Here’s a quick guide to protecting your batteries:

Following these steps will go a long way in safeguarding your investment and ensuring your products remain reliable and safe.

How to maximize NMC battery life?

Your product's battery life isn't living up to its promise. This leads to poor reviews and frustrated customers who feel let down by your brand's quality and reliability.

To maximize the cycle life of an NMC battery, avoid the extremes. Try to keep the charge level between 20% and 80%, minimize its exposure to high temperatures, and rely on a smart BMS to manage charging. The most critical factor, however, is starting with high-purity, well-made cells from the beginning.

Maximizing battery life isn't just about how long it lasts on a single charge; it's about how many charge and discharge cycles it can endure before its capacity significantly drops. This is known as cycle life. A battery that promises 1000 cycles but is treated poorly might only give you 300.

The most effective strategy is practicing "shallow cycling." This means you avoid draining the battery to 0% or charging it to 100% all the time. Keeping it in the 20% to 80% range is much less stressful for the battery's chemistry. It’s like how a person who avoids extreme physical exertion stays healthier for longer. A smart BMS can even be programmed to manage this automatically.

Temperature also plays a huge role in aging. Every time a battery gets hot, its internal chemistry degrades a little faster. This degradation is permanent and cumulative. Over time, it leads to a noticeable loss of capacity.

But now, maximizing battery life is more than just good practice—it's becoming a legal necessity. In the European Union, new regulations are being enforced that I call the "battery passport." Soon, you will be required to have a digital record of your battery's entire life, from its origin materials to its current health status. If a batch of your products shows premature failure or swelling, you won't be able to hide it. Regulators could demand a full recall, effectively banning your product from the market. A cheap battery that fails early could cost you access to the entire European continent. This is why partnering with a manufacturer who understands and prepares for these regulations is critical for your future. At Litop, we are already building our batteries and our quality systems to meet these future compliance needs.

Conclusion

In short, battery swelling is caused by gas from internal chemical reactions, often due to poor quality cells, overcharging, or heat. Prevention is your only option. Use a quality BMS, manage temperatures, and most importantly, partner with a transparent manufacturer who can prove the quality of their cells.