What Type Of Battery In Power Bank?
Most power banks use lithium batteries. There are two main types you'll typically find: lithium-ion (Li-ion) and lithium-polymer (Li-polymer or LiPo). Power bank cells are mainly divided into 18650 cells and polymer cells. The most common one on the market is 18650 lithium-ion batteries, with a market share of 70%.
Lithium-Ion vs. Lithium-Polymer Battery Cells
- Lithium-Ion (Li-ion)
- These are cylindrical batteries that look like oversized AA batteries and are commonly found in many electronics, including laptops and smartphones. Common models include 18650 and 21700. The technology of 18650 batteries is relatively mature, with a stable battery structure, high specific capacity, and outstanding comprehensive performance. However, its safety is worse than that of polymer lithium batteries, and the number of cycles of the cells is low, about 300 times.
- Lithium-Polymer (Li-polymer or LiPo)
- These use a gel-like electrolyte and are flatter, flexible, and lighter compared to Li-ion. They allow power banks to have sleek and slim designs. Common models include 606090 and 1260100. Lithium polymer battery cells use a polymer electrolyte instead of a liquid one, offering flexibility in shape and size.
- Lithium Iron Phosphate (LiFePO4)
- Lithium iron phosphate battery cells are known for their excellent thermal stability and safety. Common models include 26650 and 32700. They are used in high-capacity and heavy-duty power banks.
Main Advantages of Polymer Batteries
- The diversity of the exterior is made, and the product using the 18650 battery is thick and large, and the shape of the millennium is unchanged.
- Long service life. There is no problem with charging and discharging more than 500 times.
- It is safe to use and is mostly used in high-end products. The safety of polymer batteries is reflected in the absence of explosions, and only bulging, spontaneous combustion, etc. may occur.
- High capacity. Under the same packaging volume, polymer batteries can store more power, so most of them are lighter and thinner, with good portability, directly improving the user's use experience.
- The disadvantage is that the cost is high, and the polymer battery of the same capacity is at least 10% more expensive than the 18650 lithium ion battery.
Why Lithium Batteries Are Used in Power Banks
Lithium batteries offer a handful of significant advantages that make them the standard choice for power banks:
- High energy density: They pack a lot of power into a compact space. Lithium batteries can store much more energy compared to traditional batteries like nickel-cadmium or lead-acid.
- Lightweight and compact: They're exceptionally light and compact, perfect for slipping into your backpack or purse.
- Longer lifespan: Lithium batteries handle more charge-discharge cycles before their capacity significantly degrades. A typical lithium battery can easily handle between 300–500 cycles before losing considerable capacity.
- Low self-discharge rate: They can hold their charge well, meaning your power bank stays ready to go even after weeks or months of sitting unused.
Comparing Lithium Battery Chemistries for Power Banks
| Battery Chemistry | Energy Density | Cycle Life | Safety Features | Applications |
|---|---|---|---|---|
| Lithium Cobalt Oxide (LCO) | High | Moderate | Good | Lightweight power banks |
| Lithium Nickel Cobalt Manganese Oxide (NCM) | High | Moderate | Improved | High-performance power banks |
| Lithium Iron Phosphate (LiFePO4) | Moderate | High | Excellent | Outdoor and industrial power banks |
Safety Risks of Lithium Batteries in Power Banks
Lithium-ion batteries in power banks can be highly flammable. If incorrectly manufactured, handled, stored or disposed of, products can catch fire, explode or vent toxic gas. Most incidents with power banks have occurred when charging a mobile phone or other device. This makes the risk of injuries higher as people tend to be close to their devices. Fires from lithium-ion batteries have also occurred in homes, offices, and waste and recycling trucks and facilities. These have led to property damage and serious injuries. A lithium-ion battery fire can be very difficult to extinguish as it may reignite. Depending on the battery size, it sometimes takes days to burn.
Lithium batteries inside power banks are generally safe if they're from reputable manufacturers. However, there are some essential safety measures to keep in mind:
- Quality control matters: Trusted brands put their batteries through rigorous safety tests, including protection against overheating, short circuits, and overcharging.
- Battery Management System (BMS): Modern power banks come equipped with a BMS, protecting against excess current, temperature fluctuations, and preventing the battery from damage.
- Proper handling: Avoid exposing your power bank to extreme temperatures, dropping it, or puncturing it. Proper handling drastically reduces any safety risks.
- Regulatory standards: Always look for products certified by regulatory bodies (e.g., CE, UL, CSA). Certification ensures the power bank meets established safety guidelines.
How to Use a Power Bank Safely
- Always use the charger and cords supplied with the power bank for recharging. If no charger or cord was supplied, check the manufacturer's instructions on suitable chargers and cords.
- Charge the power bank on non-flammable surfaces such as concrete, ceramic or steel.
- Allow the power bank to cool after use and before recharging.
- Store the power bank in a cool, dry place and out of direct sunlight.
- Never use a power bank that is damaged, overheating, swelling, leaking or venting gas.
- Never charge power banks on flammable materials such as beds, sofas or carpet.
- Don't leave a power bank in a parked vehicle.
Understanding Power Bank Capacity: MAh and Watt-Hours
Battery banks are commonly rated based on their raw cell capacity in mAh. A 10,000mAh battery pack usually means there are 3.7V Li-ion cells inside the pack and they will have 37Wh of energy in them. The USB output of the pack is 5V. In most power banks, there is a circuit in the pack that steps the voltage up from 3.7V to 5V. You will not get 10,000mAh of 5V output (that would be 50Wh) from a 3.7V 10,000mAh (37Wh) battery.
Watt-hours is what matters, not mAh. A 3.7V Li-ion cell with 3000mAh can provide 11.1Wh of energy. A 12V battery with 3000mAh can provide 36Wh of energy. The capacity in mAh is only useful if you know and take into account the voltage.
Emerging Battery Technologies for Power Banks
- Graphene Battery Cells
- Graphene batteries are an emerging technology that promises high conductivity and fast charging capabilities. Pros: excellent electrical conductivity, rapid charging times, high durability. Cons: still in developmental stages, high production costs.
- Solid-State Battery Cells
- Solid-state batteries replace the liquid electrolyte with a solid one, offering higher energy density and improved safety. Pros: higher energy density, improved safety, longer lifespan. Cons: technological and production challenges, higher initial cost.
- Zinc-Air Battery Cells
- Zinc-air batteries use oxygen from the air as a reactant, providing a high energy density at a low cost. Pros: high energy density, low cost, environmentally friendly. Cons: limited rechargeability, complex air management system.
Travelling with a Power Bank: Capacity Limits
Airlines require lithium battery power banks to be placed in your carry-on bag or personal item, not in checked luggage. Keep the power bank in a spot where you can access it easily, as airport security may ask you to take it out for inspection during screening.
- Up to 100Wh (approximately 27,000mAh): Allowed without restrictions on most airlines.
- Between 100Wh–160Wh: Typically permitted but limited to two per passenger; airline approval may be required.
- Above 160Wh: Generally prohibited on commercial flights.
A lithium battery in a power bank usually lasts about 300 to 500 charge cycles before you notice a drop in performance, which generally means it will hold around 80% of its original capacity. For the average user, this translates to roughly 3–4 years of regular use. The actual lifespan depends on factors like how often you fully deplete and recharge it, the quality of the battery, and how well you care for it. Avoiding extreme temperatures and not leaving it plugged in for extended periods can help it last longer.
