Smartphone Charging: Is 100% Green Light Not Fully Charged? [Reading Science]

Even if you charge your smartphone to 100%, it is not considered fully charged. It is up to the user to decide whether to charge it for an additional 1 to 2 hours to reach a fully charged state. This is because full charging affects the battery's lifespan.
[Photo by YouTube screen capture]

[Asia Economy Reporter Kim Jong-hwa] We have now entered an era where living without a smartphone is impossible. If you leave your smartphone at home when going out, you cannot even take the bus or subway, and you find yourself in a terrible situation with no money or cards on hand. It is no exaggeration to call this the era of 'phone-body unity.'

In 2018, the Cambridge Dictionary in the UK selected 'Nomophobia' as the word of the year, referring to the phenomenon of feeling anxious without a smartphone. Nomophobia is an abbreviation of 'No mobile phone phobia.' If compared to a disease, it could be described as 'smartphone panic disorder.'

Cambridge stated, "As users perceive highly advanced smartphones as part of their body, modern humans experience a shaken sense of identity as an individual when they lose their smartphone."

As a result, some people feel more anxious as their smartphone battery gauge drops. Most people check if their smartphone battery is fully charged before leaving the house. If the battery gauge is below 100%, they charge it fully to 100% before heading out.

However, if you glance at your phone while waiting for the bus and see the battery level drop below 80%, or if it falls to around 60% before reaching your destination, anxiety begins to set in. Even though you charged it fully to 100%, why does the battery drain so quickly?

It is easy to assume that the battery life has ended, but in reality, it is more likely that the battery was not fully charged. When the charger reaches 100%, the red light turns off and the green light turns on. People then think the battery is fully charged and unplug the charger.

The problem lies here. Even if the green light is on and the battery gauge shows 100%, it does not mean the battery is fully charged. The charging rate is displayed by measuring voltage, but since it is impossible to measure the voltage of every single lithium-ion inside the smartphone battery, this phenomenon occurs.

In other words, when the green light indicating 100% charge is on, only the surface of the battery is charged, and the inside is not fully charged. To put it differently, the lithium molecules on the battery surface are 100% charged, but those inside are only about 70-90% charged. Of course, this figure can vary depending on the smartphone model and age.

Therefore, it is advisable to keep the charger plugged in even after the green light turns on. To fully charge the inside, you should leave it plugged in for another 1-2 hours after the green light appears. This is because the lithium ions inside the battery need time for the concentration gradient to even out and the voltage to sufficiently diffuse.

For batteries older than one year, the internal performance deteriorates, so the longer you keep it plugged in, the more it charges. One thing to keep in mind is overcharging. Smartphones have built-in functions to prevent overcharging, so it is generally not a big concern. However, when using non-genuine chargers, there is a risk of explosion, so extra caution is necessary. Using genuine chargers is safer and provides peace of mind against overcharging.

Some people wait until their smartphone battery is critically low before charging, while others charge it proactively. Which approach is more advisable?
Photo by YouTube Screenshot

However, there is one issue to consider: battery 'lifespan.' It is said that maintaining the charge gauge between 60-80% significantly extends battery life because the battery experiences less stress. The shortest lifespan, or the most stressful situation for the battery, is when you use it until the charge gauge hits 0% before recharging.

Older batteries such as lead-acid or NiCad batteries used before lithium-ion batteries were better off being fully discharged before charging. However, lithium-ion batteries do not have the 'memory effect' that remembers usage patterns like older batteries, so using them that way actually damages the battery. It is better to charge them frequently before they reach 0%.

However, using the battery this way lowers its 'utilization.' Utilization refers to how long you can use your smartphone after charging it at home. It measures how long you can use it after a full 100% charge. To increase utilization, it is advantageous to keep the charger plugged in for 1-2 hours even after the green light turns on.

On the other hand, considering battery lifespan, full charging itself stresses the battery. Ultimately, it is a matter of choice. If you want to use your battery for a long time without problems, maintain the charge between 60-80% during regular use. If you want to use your phone for a long time on a single charge without worrying about battery life when going out, keep the charger plugged in even after the green light turns on and fully charge it.