Battery power constantly runs applications on a daily basis to perform a wide variety of functions. Yet, there will be certain instances where battery packs will be stored for short-term and long-term periods. This situation may occur due to infrequent use of the equipment or when storing extra battery packs.
When placed into storage, the energy in the battery cells typically goes through a self-discharge. The rate of this self-discharge depends on a variety of factors, such as the battery's chemistry, the environment, and room temperatures. Using the appropriate battery storage management and charge management requirements for the battery packs may help to extend the life of your battery packs.
Custom battery packs stored in a climate-controlled environment prior to shipping.
Shelf Life for Batteries and Battery Packs
Most customers desire a battery pack with chemistries that have a slow self-discharge and an extended shelf-life. Yet, the application itself, its power needs, and the budget may dictate which battery chemistry works best for certain situations. Here is a brief overview of battery shelf life based on its chemistry when stored in optimal conditions and maintained properly.
Rechargeable Alkaline: The chemistry has an extremely low self-discharge rate of less than 0.5% each month. Battery shelf life for these packs is about 4-7 years.
Nickel-Cadmium: This has a fast discharge rate of 10% within 24 hours and then 10% per month. These batteries have a shelf life of about 1-3 years.
Nickel-Metal Hydride: The battery chemistry can have a low to high self-discharge rate based on the manufacturer. They may self-discharge up to 30% per month, yet some chemistries may keep a charge of 75% for anywhere from 1-3 years. The shelf life for this nickel-based battery is 3-5 years.
Lithium-Ion: Lithium-ion chemistries have slow self-discharge rates of 5% in 24 hours and 1-2% per month. They have a roughly 2-year shelf life.
Lithium-Polymer: This type of lithium-based battery has a self-discharge of 5% per month and a long shelf life but could go bad in as short as 18 months in poor conditions.
Lead-Acid: Lead-acid batteries have a self-discharge rate of about 5% per month. They may last anywhere from 6 months to 4 years in storage.
Keep in mind that lithium-based batteries are bare, meaning they do not come with integrated circuitry (IC), have slow discharge rates, and may last for up to 4 years or more. When ICs are added to the battery pack, they will draw small amounts of power when packs are stored to perform specific battery management system (BMS) tasks such as monitoring the state of charge (SoC). Lithium-based chemistries with ICs may self-discharge at rates of 3%.
Battery Storage Recommendations
To extend the life of batteries, many people may assume that charging the battery completely before placing it into storage is the right move. However, keep in mind that some battery chemistries do not always require to be at a fully charged state. The battery pack may be discharged or kept at a partial charge state. Also, there are certain temperature ranges that may be suitable for specific battery packs.
Lead-Acid
Lead-acid batteries should be stored in a fully charged state. When the battery begins to discharge fully or partially, it will form lead sulfate on the electrodes that eventually causes a permanent capacity loss. To avoid sulfation, the battery cells should be constantly monitored to determine their SoC and be topped off to keep their fully charged state. While you often hear that batteries should be frozen to help extend shelf-life, lead-acid chemistries should never be frozen or allowed to freeze. Optimal room temperature changes for storage purposes should remain at 50° Fahrenheit or less.
Lithium-Ion/Polymer
Lithium-based batteries can be discharged, yet these chemistries should never drop below 2.0v or they will experience permanent damage. A partial charge is acceptable for these batteries. Monitoring the charge of the battery and topping it off can extend the battery life; avoid overcharging the battery over 4.1v. Possible temperature ranges for lithium-ion batteries range from -4° Fahrenheit to 140° Fahrenheit. If the battery pack will be placed into long-term storage, room temperatures of 5° Fahrenheit to 77° Fahrenheit are recommended. Also, avoid leaving the battery pack in a constantly charged state by having the equipment or product plugged into an outlet when not in use.
Nickel-Cadmium
Nickel-cadmium chemistries are very versatile when it comes to storing at different charges. They may be discharged or charged. If you plan to store the batteries for very long periods of time, roughly three deep discharge cycles can be used to help the nickel-cadmium batteries to get back up to full capacity. To prolong the life of the batteries, the room temperatures should be set from -4° Fahrenheit to 113° Fahrenheit.
Nickel-Metal Hydride
Nickel-metal hydride has basically the same storage requirements as nickel-cadmium chemistries. They may be stored in charged or discharged states and will need recharging when taken out of prolonged storage. The room temperatures can range from -4° Fahrenheit to 113° Fahrenheit. Many batteries will need to be recharged when taken out of deep storage. Checking the charge before topping the batteries off is recommended to prevent overcharging which could permanently damage the battery. Also keep in mind that when the batteries are stored at higher temperatures, they will experience a more rapid discharge rate. An optimal temperature range to store batteries may be around 35° Fahrenheit to 40° Fahrenheit for most battery chemistries. Consider placing the battery packs in a climate-controlled environment that is dry.
Summary
Understanding the battery chemistry in the battery pack ensures that you can select the right storage requirements. Always avoid storing and then forgetting about battery packs. Regularly inspect the batteries to determine their state of charge and to evaluate if there is any damage that could cause the battery to malfunction or explode. Dispose of damaged battery packs based on the manufacturer's instructions if you notice any damage. Never use battery packs that have been improperly stored or damaged as they may experience thermal runaway, short circuits, fires, or explosions that may endanger people and equipment.
