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Comprehensive Guide to Battery Storage, Discharge, and Expiration

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Understanding the proper storage, discharge, and expiration of batteries is crucial for maximizing their lifespan and ensuring safety. Different types of batteries—nickel-based (Ni-MH and Ni-CD), lithium, alkaline, and lead acid—require specific care and handling. In this guide, we delve into the key aspects of battery storage, capacity loss, and regulations for shipping and travel.

Key Terminology

Battery Expiration

Battery expiration differs significantly from food expiration. It denotes the manufacturer’s inability to guarantee full charge beyond a certain date. Typically, a battery is considered expired when its self-discharge exceeds 20%. This date is often clearly marked on the packaging or the battery itself.

Battery Self-Discharge Rate

Self-discharge is the process where a battery loses its charge over time, even when not in use. The rate of self-discharge varies based on the battery’s chemistry, brand, storage environment, and temperature.

Battery Shelf Life

Shelf life refers to the duration a disposable battery retains its charge unused, or for rechargeable batteries, how long before it requires a recharge. It is closely related to the self-discharge rate.

Battery Storage Guidelines

General Storage Recommendations

Temperature

The ideal storage temperature for most batteries is around 59°F (15°C) with low humidity. Extreme temperatures can negatively impact battery performance:

  • Cold Storage: -40°F (-40°C) to 32°F (0°C) – While some batteries, like lead acid, won’t freeze, cold temperatures can affect their chemical composition.
  • Hot Storage: 77°F (25°C) to 122°F (50°C) – High temperatures accelerate self-discharge and can stress the battery.

Contact with Other Materials

Batteries should never come into contact with metallic items or other batteries to avoid the risk of short-circuiting. Ideally, store batteries in their original packaging or wrap them individually in plastic.

Specific Battery Types

Nickel-Based Batteries (Ni-MH and Ni-CD)

Storage

Store Ni-MH and Ni-CD batteries at about 40% state of charge (SoC) to minimize capacity loss while maintaining operational readiness. Although they can be stored fully discharged without adverse effects, a partial charge allows for faster priming.

Capacity Maintenance

Ni-MH batteries can withstand 3–5 years of storage, even at zero voltage. Priming may be necessary if voltage drops below 1V/cell, which can help reverse some capacity loss.

Lithium Batteries

Storage

Lithium-ion batteries should be stored in a charged state, ideally at 40% SoC. These batteries exhibit minimal self-discharge below 4.0V at 68°F (20°C). Rechargeable lithium-ion batteries, such as 18650 cells, can last up to 10 years with minimal capacity loss when stored at 3.7V.

Precautions

Avoid letting Li-ion batteries drop below 2V/cell for extended periods to prevent copper shunt formation, which can lead to instability and safety issues. Dispose of any lithium-ion battery that remains below 2.00V/cell for more than a week.

Alkaline Batteries

Storage

Store alkaline batteries at cool room temperatures with about 50% relative humidity. Modern alkaline batteries can retain their charge for up to 10 years if kept away from extreme temperatures.

Lead Acid Batteries

Storage

Charge lead acid batteries before storage. They can be stored for up to 2 years, but periodic monitoring and recharging when the SoC falls below 70% is recommended. Sulfation can occur with low charge, impeding current flow and reducing capacity.

Maintenance

A topping charge or elevated voltage application can mitigate early-stage sulfation. Ensure the power supply used has current limiting to prevent damage.

Capacity Loss Analysis

All batteries experience self-discharge during storage. The table below shows how temperature and SoC affect different battery chemistries over a year:

Temperature Lead Acid (Any SoC) Nickel-Based (100% SoC) Lithium-Ion (40% SoC) Lithium-Ion (100% SoC)
32°F (0°C) 97% 99% 98% 94%
77°F (25°C) 90% 97% 96% 80%
104°F (40°C) 62% 95% 85% 65%
140°F (60°C) 38% (after 6 months) 70% 75% 60% (after 3 months)

Secondary Capacity Loss

Secondary capacity loss, which is not recoverable, can occur due to:

  • Prolonged exposure to unfavorable temperatures.
  • Keeping fully charged devices plugged in.
  • Storing batteries outside their recommended SoC range.

Shipping Regulations for Batteries

Storing and shipping lithium-ion batteries partially charged reduces volatility. Removable Li-ion battery packs should be shipped at 30% SoC, as mandated by IATA and FAA. For device-integrated Li-ion packs, achieving a 30% SoC is less critical but still recommended.

Conclusion

Proper storage and handling of batteries extend their lifespan and ensure safety. By adhering to the guidelines outlined for different battery chemistries and understanding the impacts of temperature, SoC, and environmental factors, you can optimize battery performance and longevity.

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