Lithium-ion batteries are rechargeable and convenient for regular use. However, there are several claims and misconceptions surrounding their proper charging methods.

Proper Charging Methods for New Lithium-ion Batteries

1. Shelf Life & Charge Cycles: A lithium-ion battery's shelf life is approximately 3 years, regardless of use. Its performance declines rapidly after around 400-500 charge cycles. The battery's lifespan is determined by whichever occurs first: reaching the 3-year mark or completing the charge cycles.


2. Overheating Concerns: Besides being sensitive to low battery levels, lithium-ion batteries are also vulnerable to overheating, particularly during charging. If your phone case doesn’t dissipate heat well and the phone becomes hot during charging, it’s advisable to remove the case.


3. Shallow Charging and Discharging: It’s best to avoid charging or discharging the battery to its maximum capacity. Charge your battery between 10%-90% and unplug it once fully charged. To maximize its lifespan, avoid prolonged usage during charging.


4. Avoid Usage During Charging: Using your phone while charging is not recommended. If necessary, it’s safer to use it when the battery is at about 50%. Using the phone when fully charged can increase the temperature, affecting the battery’s longevity.

Detailed Explanation of the Lithium-ion Battery Charging Process

The ideal charging process for lithium-ion batteries occurs in four stages: trickle charging, constant-current charging, constant-voltage charging, and charging termination.

1. Trickle Charging: Used for recovering fully discharged battery cells. When the battery voltage is below approximately 3V, a constant current up to 0.1C is applied.


2. Constant-Current Charging: When the battery voltage surpasses the trickle charging threshold, constant-current charging starts with currents ranging from 0.2C to 1.0C. The current doesn’t need to be very precise; a quasi-constant current is acceptable.


3. Constant-Voltage Charging: When the battery voltage reaches 4.2V, constant-current charging ends, and constant-voltage charging begins. For optimal performance, the voltage tolerance should remain within +1%.


4. Charging Termination: Unlike nickel-based batteries, continuous trickle charging is not suitable for lithium-ion batteries as it may cause lithium plating, leading to instability and rapid battery degradation. Charging is terminated in two common ways:
   
   
   • By monitoring the charging current during the constant-voltage phase, stopping when the current drops to 0.02C to 0.07C.
   
   
   • By timing the charging process from the start of the constant-voltage phase, terminating after two hours.

This four-stage charging process typically takes about 2.5 to 3 hours to fully charge a completely discharged battery. Advanced chargers also include additional safety features.

Fast Charging for Convenience, Slow Charging for Longevity

Apple’s lithium-ion batteries utilize fast charging to reach 80% capacity quickly and then switch to slower trickle charging. The time taken to reach 80% depends on various factors such as settings and charging equipment. If the battery exceeds recommended temperature limits, the software may limit charging after 80%, promoting both convenience and longevity for the battery.

Making Charging Easier

Apple’s lithium-ion batteries allow for flexible charging at any time without needing to discharge them to 100% first. A charge cycle is completed when 100% of the battery’s capacity is used, but not necessarily in a single charge. For instance, if you use 75% of the battery's capacity one day, fully charge it overnight, and use 25% the next day, you complete one charge cycle over two days. Multiple days may be needed to complete a full cycle. While the battery’s capacity decreases slightly with each cycle, Apple’s lithium-ion batteries retain at least 80% of their original capacity after numerous charge cycles, with variations depending on the product.

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