Should You Store Lithium Batteries Fully Charged or Empty?

Storing lithium batteries incorrectly can ruin them, costing you money and delaying your projects. You need a clear, reliable method to protect your investment and ensure performance.

You should never store lithium batteries fully charged or completely empty. The ideal storage state of charge (SOC) is between 40% and 60%. This minimizes capacity loss and prevents permanent damage, ensuring the battery is ready for use when you need it.

That's the short answer. But if you're like me, you want to know why. The details matter, especially when your products and reputation are on the line. The type of battery, the storage time, and even the temperature¹ all play a huge role. Let's break it down so you can make the best decisions for your inventory.

Is it okay to store lithium-ion batteries fully charged?

You might think a full charge means it's ready to go. But storing batteries at 100% actually hurts them over time, reducing their lifespan and reliability.

No, it is not okay to store lithium-ion batteries fully charged. Keeping a battery at a 100% state of charge puts it under high stress, which accelerates chemical degradation. This leads to faster capacity loss and a shorter overall lifespan for the battery.

A fully charged battery is like a stretched rubber band. It's full of potential energy, but it's also under constant tension. For a lithium-ion battery, this high-voltage state accelerates unwanted chemical reactions inside the cell. The electrolyte can break down, and a layer can form on the electrodes. This process is a normal part of battery aging, but high voltage speeds it up dramatically.

Think of it this way: every day you store a battery at 100%, you are essentially "using" up a small part of its life, even if it's just sitting on a shelf. This damage is permanent. Over a few months, you could lose a significant percentage of the battery's original capacity.

I remember a client who insisted on receiving their batteries fully charged. They thought it would save them a step in their production line. We at Litop advised against it, but they were firm. Six months later, they called us. Their new medical devices² weren't meeting the advertised battery life. We had them send back some of the unused batteries from that first shipment. Our tests showed they had lost nearly 15% of their capacity just from sitting on the shelf. Storing them at 50% would have resulted in a loss of only 2-3%. That experience was a costly lesson for them, but it highlights just how critical proper storage is. Storing at full charge is simply not worth the convenience. It degrades your assets before you even use them.

What is the 80 20 rule for lithium batteries?

You have probably heard the "80/20 rule" for productivity, but what about for batteries? This simple guideline can cause confusion. It's often misunderstood, especially when it comes to storage.

The 80/20 rule for lithium batteries is a guideline for daily use, not long-term storage. It suggests keeping the battery's charge between 20% and 80% to maximize its cycle life. For storage, the ideal range is much narrower, typically between 40% and 60%.

The 80/20 rule is excellent for devices you use every day, like a phone or a laptop. By avoiding the extremes of 0% and 100%, you reduce stress on the battery. This helps you get more charge cycles out of it over its lifetime. But this rule is for active use, not for inventory sitting on a shelf.

Here's where a common misconception comes in. Many of my customers see that we, as manufacturers, ship batteries at around a 30% state of charge (SOC). They naturally assume this must be the best level for storage. This is incorrect. The 30% SOC is a requirement set by international air transport regulations (IATA) for safety. A lower charge state reduces the energy in the battery, making it safer to transport. It's a safety baseline, not an optimal storage guideline.

Storing a battery at 30% for a long time is risky. All batteries self-discharge, meaning they slowly lose charge over time. If you start at 30% and let it sit for months, the voltage can drop to a critically low level. Once it drops below a certain point, the battery's internal protection circuit may kick in. This puts it into a "sleep mode" from which it might not wake up. Or worse, the cell chemistry can be permanently damaged. This is called over-discharge. A 40-60% SOC gives you a much larger safety buffer against self-discharge.

What is the best way to store lithium batteries?

You need your batteries to perform perfectly when you finally use them. Improper storage can lead to dead batteries and project delays. So what is the foolproof method?

The best way to store lithium batteries is at a 40-60% state of charge in a cool, dry place, ideally around 15°C (59°F). The battery chemistry also matters. LiFePO4³ (LFP) batteries are more stable and can be stored at a slightly higher charge.

Getting storage right is a combination of three factors: charge level, temperature, and battery chemistry. We've established that a 40-60% SOC is the sweet spot. Now let's talk about temperature. Heat is the enemy of batteries. For every 10°C (18°F) rise in temperature, the rate of chemical reactions inside the battery roughly doubles. This means a battery stored at 30°C (86°F) will age twice as fast as one stored at 20°C (68°F). The ideal storage temperature is cool, around 15°C (59°F). A climate-controlled warehouse is best. Never store batteries in direct sunlight or a hot car.

The type of battery you are using is also a critical piece of the puzzle. Not all lithium-ion batteries are the same. The two most common chemistries we work with at Litop are NMC⁴ (Nickel Manganese Cobalt) and LFP (Lithium Iron Phosphate). NMC is popular for its high energy density, making devices smaller and lighter. But LFP is the champion of longevity and safety, especially for storage.

LFP batteries are much more tolerant of storage conditions. They have a lower self-discharge rate and are less stressed at higher states of charge. For an LFP battery, you can comfortably store it between 50% and 80% SOC without much worry. This is a huge advantage for inventory management. NMC batteries, on the other hand, are more sensitive and should be kept closer to that 40-60% range.

For my clients in the medical device field, I almost always recommend LFP for products that might sit in storage for a while. The stability and safety are non-negotiable.

How long can a lithium-ion battery sit unused?

You have batteries in your warehouse, but your project is delayed. Now you're worried. How long can they sit before they become useless? The answer is not simple.

A lithium-ion battery can sit unused for 6 months to a year without major damage, provided it's stored properly at 40-60% charge in a cool environment. However, you should check and recharge it back to the ideal level every 3-6 months to be safe.

The shelf life of a lithium-ion battery depends entirely on its storage conditions and its chemistry. A battery is always losing a little bit of charge. This process is called self-discharge. The speed of this process depends on the battery's health, its chemistry, and especially the temperature.

A typical NMC battery might lose 1-3% of its charge per month when stored at the ideal 50% SOC and 15°C. But if you store that same battery at 35°C (95°F), the self-discharge rate could jump to 5-10% per month. If it was stored at 100% charge at that high temperature, you'd see significant permanent capacity loss on top of the self-discharge.

This is another area where LFP batteries shine. Their self-discharge rate is incredibly low, often less than 1% per month under ideal conditions. This means you can store an LFP battery for over a year with minimal need for maintenance. An NMC battery needs more attention. I advise my clients using NMC batteries to check the voltage and top them up back to 50% every 6 months at a minimum. For LFP, checking once a year is often sufficient.

Here's a simplified look at what you can expect in terms of permanent capacity loss from storage alone over one year at 25°C (77°F):

As you can see, the combination of a lower storage charge and a more stable chemistry like LFP makes a massive difference. It's the key to ensuring your battery inventory remains a valuable asset, not a ticking liability.

Conclusion

To maximize battery life, store lithium batteries at 40-60% charge in a cool, dry place. Avoid storing them full or empty. For superior stability and longer shelf life, consider using LiFePO4 (LFP) batteries, as they are more forgiving during long-term storage.