Lithium polymer (LiPo) batteries have become very popular in recent years for powering everything from consumer electronics to electric vehicles. However, there has been some debate around the best practices for storing these batteries when not in use. Some argue that LiPo batteries should be stored at full charge to keep them fresh and ready for use. Others believe fully charging LiPos before storage can reduce their lifespan and even pose safety risks. In this article, we will examine the advantages and disadvantages of storing LiPo batteries fully charged versus partially charged. We will look at how storage conditions impact the battery’s performance and longevity as well as best practices recommended by manufacturers. With the pros and cons laid out, you can make an informed decision about the optimal charge level for your LiPo battery storage needs.
What are LiPo batteries?
LiPo batteries are a type of lithium-ion battery that uses a polymer gel electrolyte instead of a liquid electrolyte. This makes the batteries lighter and able to be packaged into more flexible shapes and sizes compared to traditional lithium-ion batteries. LiPos have higher energy density than other rechargeable battery chemistries, meaning they can store more energy per given volume. They also have relatively low self-discharge, retaining 85-95% of their charge after 30 days of storage.
Some key advantages of LiPo batteries:
- High energy density – more power storage capacity per weight
- Low self-discharge – retain charge well during storage
- Lightweight and versatile form factors
- High discharge rates – can deliver energy quickly
- No memory effect – batteries do not need periodic full discharges
Because of these beneficial characteristics, LiPo batteries have become the preferred rechargeable battery option for many applications including:
- Radio controlled vehicles like drones, planes, boats, cars
- Portable electronics like laptops, tablets, smartphones
- Electric vehicles
- Power tools and motorized equipment
- Backup power supplies
Understanding LiPo battery chemistry and how to properly care for them is important to maximizing performance and lifespan.
Should LiPo batteries be stored fully charged?
When LiPo batteries are not being used, proper storage is key to preserving battery health. There are two main schools of thought regarding storage charge level:
Pros of Full Charge Storage
- Batteries will be fresh and ready for immediate use
- May help prevent growth of lithium metal deposits called dendrites during storage that can damage cells
- Slows self-discharge so batteries retain close to full charge longer
Cons of Full Charge Storage
- Puts more strain on electrodes leading to faster capacity fade over time
- Increased risk of swelling or damage from electrolyte decomposition
- Safety hazard if stored batteries are damaged, experience short circuit, etc.
Pros of Low/Mid-level Charge Storage
- Less strain on electrodes leading to longer overall battery lifespan
- Reduces risk of damage from swelling or internal shorts
- Safety hazard from damaged batteries is reduced
Cons of Low/Mid-level Charge Storage
- Batteries will need to be charged before use
- May discharge more quickly during storage
- Possible increased risk of lithium metal dendrite formation
There are good arguments on both sides. To make an informed decision, it helps to dive deeper into what happens inside LiPo batteries and how storage conditions impact their health and performance over time.
LiPo Battery Chemical Reactions
LiPo batteries work by moving lithium ions between a positive electrode (cathode) and a negative electrode (anode), generating a flow of electrical current in the process. The cathode is typically made of lithium metal oxide, while the anode is made of porous carbon. The electrodes are separated by the polymer electrolyte layer that allows lithium ions to flow back and forth.
Charging
During charging, an external power source applies a higher electrical potential to the cathode. This causes the lithium ions to leave the cathode, travel through the electrolyte layer, and insert themselves into the carbon anode. The electrons flow through the external circuit to balance the charge transfer.
Discharging
To generate power, the process is reversed. The lithium ions flow from the anode back to the cathode releasing electrons that travel through the external circuit, powering the connected device.
Effects of Storage at Full Charge
When a LiPo battery is fully charged, the anode is stuffed full of lithium ions and the cathode has a minimal amount left. This state creates strain on the anode structure and electrolyte over time. The anode is being pushed to its limits of lithium ion capacity.
Storing in this condition can start to cause swelling of the anode, decomposition of the electrolyte, and loss of performance. The electrode material may begin to fracture or breakdown gradually reducing capacity each charge cycle.
The likelihood of swelling, internal short circuits, and dendrite formation is also increased at higher charge states. This not only reduces usable capacity faster but poses safety risks if damage to the battery occurs.
Effects of Storage at Partial Charge
Storing LiPo batteries at a partial charge of 40-60% is generally considered optimal for longevity. At this stable mid-point charge, there is much lower strain on the anode and electrolyte compared to full charge.
The cycling of lithium ions back and forth occurs over a smaller range requiring less expansion and contraction of the anode. This puts less stress on the internal structure preserving the battery’s capacity for more recharge cycles.
Research has shown storage at reduced state-of-charge can significantly extend the usable lifespan of LiPo batteries. There is also decreased risk of swelling, short circuiting, and dendrite formation at lower charge levels. The tradeoff is that batteries will require recharging before use.
LiPo Charge and Discharge Best Practices
In addition to proper storage, following good general practices for charging, discharging, and using LiPo batteries can help maximize their life and safety:
- Avoid fully discharging batteries before recharging
- Do not leave batteries discharged for extended periods
- Charge using a LiPo compatible charger only
- Follow manufacturer recommended charge/discharge rates
- Avoid charging batteries unattended
- Stop use if batteries become excessively warm, swollen, or damaged
- Avoid short circuiting battery terminals
Adhering to responsible usage and storage goes a long way to preserving your investment in LiPo batteries.
LiPo Storage Temperature Considerations
In addition to charge level, ambient temperature during storage also impacts LiPo battery health. Storing batteries at extreme temperatures can accelerate chemical decomposition and capacity loss.
LiPo battery electrolyte works best within an optimal temperature range. At low temperatures, the electrolyte can become too stiff for lithium ions to flow freely. High temperatures make the electrolyte more liquid causing increased reactions.
Most LiPo batteries perform best when stored long-term in the range of 10-25°C or 50-77°F. Temperatures outside this window for over 2 weeks can start to reduce battery life. Storing LiPo batteries in a controlled environment when possible is recommended.
Low Temperature Effects
Storing LiPo batteries below freezing causes the electrolyte to become stiff and congealed. This prevents the normal flow of lithium ions and can temporarily reduce available capacity. Prolonged exposure to freezing temperatures risks damage to the cell structure.
Bringing batteries back to room temperature restores the electrolyte mobility and performance. However, permanent loss of capacity may still result from lengthy frozen storage.
High Temperature Effects
Excessive heat accelerates the degradation of LiPo battery components. High temperatures increase electrolyte evaporation and reactivity while accelerating the breakdown of electrodes. Storing LiPo batteries above 30°C/86°F long-term can quickly lead to permanent battery damage.
The risk of thermal runaway also increases at elevated temperatures. This is a dangerous positive feedback loop where rising temperatures inside the battery cause progressively faster breakdown reactions. Thermal runaway can result in catastrophic failure with fires, explosions, and extreme heat generation. Proper storage conditions reduce this risk.
Conclusion
Finding the optimal balance between readiness, longevity, and safety requires understanding the tradeoffs around LiPo battery storage. While there are some advantages to keeping batteries fully charged, the negatives tend to outweigh the positives for most users.
Storing LiPo batteries at a 40-60% charge level in a temperature controlled environment provides the best combination of performance, lifespan, and risk reduction. With proper usage and storage, LiPo batteries can deliver years of reliable power across a wide range of applications. Just be sure to educate yourself on their care and handling to get the most return on your investment.
