You've stocked up on lithium batteries, but are they losing value on the shelf? Unused batteries degrade over time, which can hurt your product's performance and your bottom line.
Yes, lithium batteries expire even if you never use them. This is due to a natural process called calendar aging, where internal chemical reactions slowly degrade the battery's components. This causes a gradual loss of capacity and an increase in internal resistance, reducing the battery's overall performance.
I remember a client, a sharp business owner named Michael, who bought a large batch of batteries for a new medical device. He stored them for nearly a year to be ready for a big product launch. When the time came, he found that a significant portion of the batteries couldn't hold a full charge. He thought he was being efficient, but the reality was that his investment was slowly fading away on the shelf. This is a common problem that many people overlook. The "shelf life1" of a battery isn't just a suggestion; it's a critical factor that directly impacts your product's quality and your company's reputation. So, how can you avoid this costly mistake? Let's get into the details of what really happens to batteries while they wait.
How long can a lithium battery sit unused?
Planning your inventory is tough. If you store lithium batteries for too long, they might fail when you need them. Let's look at the factors that determine their shelf life.
Typically, a standard lithium-ion battery2 can be stored for 2-3 years under ideal conditions. However, this lifespan varies greatly based on the battery's chemistry, its state of charge during storage, and the ambient temperature. LiFePO4 batteries3, for example, have a much longer shelf life, often lasting over 5 years.
The question of how long a battery can sit on a shelf is one I get almost daily. The answer isn't a single number; it's a balance of three critical factors: chemistry, temperature, and charge level. Getting this balance right is the key to preserving your battery inventory and protecting your investment. It’s not just about letting them sit; it’s about storing them smartly.
The Role of Chemistry and Temperature
Different types of lithium batteries age at different rates. For instance, Lithium Iron Phosphate (LiFePO4) batteries are champions of longevity. They are more chemically stable, so they degrade much slower in storage compared to chemistries like Lithium Cobalt Oxide (LCO) or NMC, which are common in consumer electronics.
Temperature, however, is the single biggest enemy of a stored battery. Heat accelerates the internal chemical reactions that cause degradation. Storing batteries at a high temperature, like in a hot warehouse during summer, can cut their shelf life in half or even more. The ideal storage temperature is cool, around 15°C (59°F). While room temperature is acceptable, cooler is always better.
The Importance of State of Charge (SoC)
You might think storing a battery at 100% charge is best, but it's actually one of the worst things you can do. A fully charged battery is at a high voltage, which puts stress on its internal components and speeds up degradation. On the other hand, storing it completely empty (0% SoC) is also dangerous. The voltage can drop so low that it causes irreversible damage, and the battery may never be able to charge again. The sweet spot for long-term storage is between 40-50% State of Charge. This middle ground minimizes stress and keeps the battery in a stable, dormant state.
New Regulations and What They Mean for You
Recently, new EU regulations have made battery transparency mandatory. Soon, batteries will need to have their manufacturing date and health status clearly available. This means you can no longer be sold "new" batteries that have been sitting in a warehouse for three years. This is a great step forward for quality control. It forces manufacturers like us at Litop and customers like you to be more diligent about inventory. It ensures that the battery going into your device is fresh and performs as expected.
How to check if a lithium battery is still good?
You found some old battery stock and need to know if they're still usable. Using them is a gamble that could damage your products or disappoint your customers. Let's talk about how to test them.
To check if a lithium battery is good, start with a visual inspection for swelling, leaks, or damage. Next, use a multimeter to measure its open-circuit voltage. For a definitive answer, a battery analyzer should be used to test its actual capacity and internal resistance against its original specifications.
When you have a batch of batteries that have been in storage, you can't just assume they're ready to go. A few simple checks can save you from major headaches like product failures or, worse, safety incidents. At Litop, we have a rigorous quality control process, and these are the same steps we take to ensure every battery that leaves our factory meets the highest standards. You can apply a simplified version of this process to your own inventory.
The Visual Inspection
The first and easiest check is a visual one. Look closely at each battery.
- Swelling or Bloating: If the battery looks puffy or swollen, it's a major red flag. This indicates that gas has built up inside due to chemical degradation. A swollen battery is a safety hazard and should be set aside for proper disposal immediately. Do not attempt to use or charge it.
- Leaks or Corrosion: Look for any signs of liquid leakage or corrosion on the terminals. The electrolyte inside is corrosive and flammable.
- Physical Damage: Check for any dents, punctures, or damage to the outer casing. Any breach of the battery's protective shell compromises its safety and integrity.
Measuring Voltage and Internal Resistance
If the battery passes the visual check, the next step is to measure its electrical properties.
- Open-Circuit Voltage (OCV): Using a simple multimeter, you can check the battery's voltage. A healthy 3.7V Li-ion cell that has been in storage should still have a voltage above 3.0V. If the voltage has dropped below 2.5V, the cell may be permanently damaged and might not be recoverable.
- Internal Resistance (IR): This is a more advanced but crucial metric. As a battery ages, its internal resistance increases. Higher resistance means the battery struggles to deliver power, leading to poor performance, especially in devices that require a lot of current. Measuring IR requires specialized equipment, but it gives a very accurate picture of the battery's health.
The Ultimate Test: Capacity Measurement
The most definitive way to know a battery's condition is to measure its actual capacity. This involves using a battery analyzer to perform a full charge and discharge cycle. The test measures how much energy the battery can store and deliver (in mAh or Ah) and compares it to its original rated capacity. As a general rule, a battery that has lost more than 20% of its initial capacity (meaning its State of Health is below 80%) is considered at the end of its useful life for most demanding applications. This is the gold-standard test we use to validate battery performance.
Do lithium batteries go bad with age?
You might think a battery is fine as long as it has not been used. But age itself is a powerful factor, and a five-year-old unused battery is not the same as a new one.
Yes, absolutely. Lithium batteries go bad with age, even if they are never charged or discharged. This natural degradation is called "calendar aging." It is an unavoidable process where slow chemical changes inside the battery reduce its ability to store energy and deliver power over time.
Many people focus on "cycle life," which is how many times a battery can be charged and discharged. But they often forget about the other side of the coin: calendar aging. This is the aging that happens just from the passage of time. A battery is a tiny chemical power plant, and like any chemical system, it changes over time. Understanding this helps you set realistic expectations for the lifespan of your products and manage your inventory effectively.
What is Calendar Aging?
Calendar aging refers to all the degradation processes that occur while the battery is at rest. It's happening right now to the battery in your phone and to the batteries sitting in a warehouse. The main culprit is the slow, continuous growth of a layer called the Solid Electrolyte Interphase (SEI) on the anode. This layer is essential for the battery to function, but as it thickens over time, it consumes lithium ions that are needed to store charge. This process is the primary reason for capacity loss in a stored battery. Other factors, like the slow decomposition of the electrolyte, also contribute. These reactions are unavoidable and happen faster at higher temperatures.
Calendar Aging vs. Cycle Aging
It's helpful to think about battery aging in two distinct ways: calendar aging and cycle aging. They are caused by different things and have different effects.
| Feature | Calendar Aging | Cycle Aging |
|---|---|---|
| Cause | The simple passage of time, storage conditions | The physical act of charging and discharging |
| When it occurs | Constantly, 24/7, even when the battery is idle | Only when the battery is being used |
| Main Impact | Gradual and permanent loss of total capacity | Wear and tear from the expansion and contraction of materials |
| Key Factors | Storage Temperature, State of Charge (SoC) | Depth of Discharge, Charge/Discharge Rate (C-rate) |
This distinction is very important. For a product that is used every day, cycle aging might be the main factor determining its battery life. But for a medical device that might sit in a clinic for months before being used, calendar aging is the real killer. I always make sure my clients understand this so they can plan for battery replacements accordingly.
How We Mitigate Calendar Aging at Litop
While we can't stop calendar aging, we can certainly slow it down. At Litop, we do this by focusing on quality from the very beginning. We select high-purity raw materials and use stable chemistries like LiFePO4 for applications that require a very long shelf life. Our advanced manufacturing processes create a more stable initial SEI layer, which reduces the rate of degradation over time. We also provide all our clients with clear guidelines on how to properly store their batteries to maximize their lifespan.
Are lithium batteries safe when not in use?
You are storing batteries in your facility, and you have a nagging concern about safety. A fire or leak in your warehouse could be catastrophic for your business and your employees.
Generally, lithium batteries are safe when not in use, as long as they are stored correctly. Proper storage means keeping them in a cool, dry place, at a partial charge, and away from flammable materials. However, damaged, defective, or improperly stored batteries can pose a significant safety risk.
Safety is the most important consideration when handling lithium batteries. While they are a reliable power source, they contain a lot of energy in a small package. When that energy is released in an uncontrolled way, it can be dangerous. The good news is that ensuring safety during storage is straightforward if you follow a few basic but critical rules. At Litop, safety is built into our design and manufacturing, but it extends all the way to how our products are stored by our customers.
Potential Safety Risks of Stored Batteries
Even when they are not being used, batteries can present hazards if handled improperly.
- Thermal Runaway: This is the most serious risk. An internal or external short circuit can cause the battery to heat up uncontrollably, leading to fire or even an explosion. This can be triggered by physical damage (like dropping a battery), a manufacturing defect, or if the terminals accidentally touch a metal object.
- Swelling and Gassing: As a battery degrades, it can generate gas internally. This causes the cell to swell. A swollen battery is a clear sign of a problem. The pressure inside increases the risk of the casing rupturing, which can release flammable electrolyte and start a fire.
- Electrolyte Leakage: If a battery's seal is compromised, the electrolyte can leak out. This liquid is both corrosive and flammable, creating chemical and fire hazards in your storage area.
Best Practices for Safe Storage
To prevent these risks, you need to create a safe storage environment.
- Control the Environment: Store batteries in a cool, dry, and well-ventilated area. Keep them out of direct sunlight and away from any heat sources like radiators or machinery. The area should be dedicated to battery storage and kept clear of flammable materials.
- Maintain Proper SoC: As we've discussed, store batteries at a partial charge of 40-50%. This is not just for longevity; it's also for safety. A fully charged battery has more energy, making any potential failure more severe.
- Isolate and Protect: Keep batteries in their original packaging whenever possible. If not, use individual plastic bags or non-conductive trays to prevent terminals from touching. Never store loose batteries in a metal bin or drawer.
- Regular Inspection: Make it a habit to periodically inspect your battery stock. Look for any of the warning signs like swelling or damage. If you find a compromised battery, remove it immediately and follow proper disposal procedures for hazardous materials.
At Litop, we ensure all our batteries pass rigorous safety tests, including the UN38.3 certification required for transportation. We provide all necessary safety documentation, like the Material Safety Data Sheet (MSDS), to ensure our clients can handle and store our products safely.
