How to Store Lithium-Ion Batteries

Lithium-ion (li ion) batteries are the most commonly used power source for all things with a rechargeable battery. Having been with us since the 1990s, li ion battery technology has steadily evolved from cell phones and laptops to electric vehicles (EVs) and utility-grade energy storage.

As with any technology, invariably there are associated risks. Li ion batteries are no exception. And as they permeate virtually every device requiring a rechargeable electric power source, these risks are becoming increasingly evident. The news and social media routinely report a dramatic fire or explosion resulting from a li-ion battery failure or thermal runaway event. While these events can be spectacular, in truth, li ion battery technology is largely safe and the dramatic incidents represent only a tiny fraction of the literally billions of li ion batteries currently in use.

While everyone should respect the risk posed by li ion batteries and treat them in a safe and responsible manner, it is businesses and companies that use multiple tools and equipment powered by li ion batteries that are often most at risk.

As this article will describe, the risk can be managed by paying careful attention to how the li ion batteries are stored.

Lithium-ion Battery Storage – General Guidelines

When storing li ion batteries, the amount of risk is based on whether the batteries are actively being charged during short-term storage or non-charging batteries are simply being stored for a longer period. Regardless, there are several measures that can be taken to reduce the risks associated with li ion battery storage.

Manufacturer instructions: Always refer to the manufacturer’s instructions on the best/safest way to store batteries and adhere to their guidance.

Storage Temperature Range: Batteries should be stored in a cool, dry place, ideally at room temperature. Extreme temperatures—i.e., low temperatures below -13° F (-25° C) or high temperatures above 149°F (65° C) –can degrade battery performance, potentially damage the battery, and increases the risk of battery failure leading to fire or explosion.

Sunlight exposure: It is best to keep stored batteries in a location where they are not exposed to direct sunlight. Direct sunlight can accelerate battery degradation and may cause internal overheating leading to failure, particularly if the battery is charging.

Humidity levels: The battery storage location should avoid areas with high humidity. Moisture from the environment can lead to corrosion and internal damage. In addition to degrading the battery, this increases the risk of battery failure at some point in the future.

Ventilation: Effective ventilation in the storage area is an integral component of all safe battery storage to help keep the batteries cool and avoid degradation. However, if the storage location is enclosed and/or the batteries will be charging while stored, proper ventilation becomes a necessity for two important reasons:

• When a battery is being charged, it could produce excessive heat. Ventilation dissipates the heat and prevents internal overheating which can cause battery failure.
• Should the battery fail for whatever reason, it will begin to emit hazardous (flammable and toxic) gases. Ventilation prevents their accumulation and reduces the creation of a potentially explosive environment.

Li-Ion Battery Positioning and Placement During Storage

Secure the batteries: Store batteries such that they are not at risk of being dropped, falling, crushed, or punctured. Physical damage can lead to internal short circuits causing battery failure.

Store batteries upright: Storing batteries upright helps:

• Prevent leaks of the flammable electrolyte in case they are not sealed properly.
• Ensure batteries equipped with venting systems work properly avoiding internal pressure buildup.
• Avoid physical damage from falls or tipping over.
• Maintain uniform distribution of electrolytes which improves service life and performance.
• Prevent internal components from shifting which can cause short circuits and battery failure.

Protect batteries from loose metal objects: Keep batteries away from loose metal objects, such as screws, nails, tools, etc. to prevent short circuits.

Maintain separation from other batteries/objects: Batteries and battery packs should never be stacked on top of each other or have items placed on top of them. Rather, batteries should be stored in a single layer or in properly designed racks that prevent them from touching or applying pressure to each other. Doing so helps avoid risks such as:

• Physical damage which can cause internal short circuits and/or leaking electrolyte.
• Battery terminals contacting each other potentially creating a short circuit and rapid discharge which generates heat and can catch fire.
• Interference with heat dissipation, particularly during charging.
• Stability problems because improperly stacked batteries are far more likely to fall or tip over.

Long-Term Battery Storage

When storing li ion batteries for periods of one month or longer, there are a few additional precautions to take that improve the batteries’ service life and performance as well as safety.

During long-term storage, batteries should never be continuously charging, nor should they be fully charged or fully discharged. The rationale for each is as follows:

• Continuously charging: Battery failure is most likely to occur during charging. Continuously charging over long periods of time greatly increases the risk. Additionally, continuous charging stresses the battery and can greatly shorten its service life.
• Fully charged: A fully charged state creates more internal stress on the battery. This can accelerate degradation of internal components and increase the risk of swelling and/or leakage. Either of these will degrade battery performance and service life and can create a safety hazard.
• Fully discharged: Li ion batteries have protection features built in that depend on a minimum voltage threshold to function properly. Storing a fully discharged battery for extended periods can cause irreversible damage which can render the battery inoperable. It can also cause conditions allowing the creation of copper filaments inside the lithium-ion cell which can lead to short circuits and battery failure.

Most battery manufacturers recommend storing batteries with a 30% to 50% state of charge (SOC) for optimal performance and service life. Interestingly, the 2024 amendments to  International Fire Code (IFC) regarding li ion battery storage grant waivers to their storage requirements when li ion batteries are stored with an SOC that does not exceed 30%. Batteries with 30% or less charge are considered less hazardous for storage purposes and have less chance of catastrophic failure.

Along with storing li ion batteries at the proper SOC, they should also be regularly monitored and inspected while in storage. The charge level of the batteries should be checked every few months. If the battery experiences self-discharge below 30%, the battery should be recharged back to not more than 30% SOC to maintain battery health.

The batteries should also be visually inspected for any signs of damage or swelling. Damaged or swollen batteries are a safety risk and should be removed and properly disposed of or recycled.

Short-Term Battery Storage

Short-term storage is considered to be a few days up to one month. While conditions such as the level of charge are not as critical, it is still recommended to store them at an SOC not greater than 30%. As with long-term storage, batteries should never be continuously charging while in the short-term.

Charging Batteries Overnight

Businesses that use li ion batteries to operate power tools and equipment during the day typically charge them overnight so they are ready for service the next day. Most modern charging systems for these types of batteries prevent overcharging and regulate battery temperature during charging. But, since most battery failures occur during charging, clearly these systems are not 100% failsafe.

As these batteries can contain a large amount of stored energy, the potential risks associated with improper handling or malfunctioning equipment are significant. To manage these risks, overnight charging should be performed with the following considerations:

• Use only the battery charger provided with the battery or device or a certified third-party charger. Aftermarket or non-certified chargers may not regulate the charge properly which could lead to overcharging/overheating and battery failure.
• Inspect the battery, charger, and associated cables and cords for any signs of damage, deformation, or loose connections. Any of these can cause a fire hazard and should not be used.
• Perform charging away from combustible items. Should a battery fail and ignite, the risk of fire spread can be greatly reduced if the battery charging location is isolated from nearby combustibles.
• Consider limiting the charging level to 80%. Always charging a battery to 100% and maintaining this level of charge for extended periods can degrade the battery. To protect the battery, some devices can be set to limit the charge to 80%.
• Be alert to overheating. If a battery gets very hot during charging, it may be a sign that the battery is beginning to fail. If this occurs, it is best to:
• Immediately stop charging.
• Move the battery to a safe location and allow it to cool.
• Observe it for smoking, swelling, or leaking; do not use the battery if any of these conditions are noticed.
• Inspect the charger for any signs of damage, corrosion, or excessive wear.
• Consult with the manufacturer. Read the operating manual for troubleshooting tips and/or call customer service for advice.
• When in doubt, do not use the battery and/or charger. If the battery is taken out of service, dispose of it properly or recycle it to prevent its reuse.

 Fire Protection Equipment and Emergency Preparedness

Despite taking all necessary precautions, the possibility remains that a li ion battery will fail and cause a fire. Just as with all fire hazards, being prepared is a critical safety task. Best practices for battery safety during storage include:

• Providing fire extinguishers and ensuring employees are trained in their use.
• Ensuring adequate smoke detectors are present as well as regularly tested.
• Having a clear plan in place for responding to a battery fire which can be difficult to extinguish and may require special handling.
• Conducting regular fire drills and ensuring employees know how to report an emergency and how to evacuate.

An innovator in fire-rated cabinets and containment systems, Justrite recognizes the threat li ion batteries can pose if they are not stored properly, especially while charging. With the Justrite Lithium-Ion Battery Charging Safety Cabinet, companies can charge and store li ion batteries with peace of mind in a cabinet conveniently designed for benchtop use.

This innovative cabinet’s advanced features include:

• Double-wall steel construction with insulating air gap: This creates an impenetrable structure that contains explosions and heat while maintaining a safe-to-touch outer shell.
• Pressure relief vent system: Vented door panels dampen the explosive force of a battery failure.
• Reinforced steel door latch plates: Steel latch rods with reinforced latch cradle plates ensure that the cabinet doors remain closed should a battery explode.
• Flame arresters. Double-layer wire-mesh flame arresters absorb heat and stop flames from escaping the cabinet
• Door hinge flame guards: These prevent flames from escaping through the door hinges, preventing secondary fires outside of the cabinet.
• Crossflow fan ventilation system: This provides a constant supply of fresh air moving though the cabinet to keep the batteries cool while charging.

• Spring-loaded dampers: Damper flaps on the ventilation system automatically close when the cabinet temperature reaches 135°F (57°C) to reduce the release of harmful smoke and gases by as much as 99%.
• Unique filtration system: The pressure relief vent system contains an integrated filter that traps smoke and absorbs toxins.
• Heat-activated expanding door seals. Intumescent seals swell as temperatures rise to prevent smoke, fumes, and flames from escaping through the door frame.

The Justrite Lithium-Ion Battery Charging Safety Cabinet is specifically designed to provide a storage environment specially suited to li ion battery storage. In the event of a battery failure in the cabinet, its design, features, and construction materials work together to contain the hazards and prevent fire and toxic gases from entering the work environment.