Fast charging is not more damaging than slow charging for smartphone batteries

Fast charging does not degrade smartphone batteries more than slow charging, as demonstrated in a two-year test that debunks one of the most common myths about this technology.

Fast charging helps reduce battery charging times, but it generates a lot of heat during use, which impacts the component. This is because smartphone batteries are mainly made with lithium ions, which are very sensitive to temperature variations and degrade when the temperature is high.

In other words, fast charging, by generating more heat, damages the battery, causing it to lose capacity over time. Therefore, it is often recommended to use a slower 5-watt charger if the phone will be plugged in for a long time or not to charge the battery beyond 80 percent nor let it completely drain before charging it again.

However, technology experts from the YouTube channel HXT Studio tested this fact with an analysis spanning two years and 40 phones, specifically iPhone 12 and iQOO 7 models.

The tests included different charging methods: one with fast charging, with models charged at 20 watts and others at 120 watts; another with slow charging at 5 watts and 18 watts; a third group charged fast between 30 and 80 percent; and a control group that was not charged for six months.

These experts measured the smartphones’ charging capacity before and after the tests and found that after 500 charging cycles, degradation among iPhones in the slow and fast charging groups was similar: the former lost 11.8 percent capacity and the latter 12.3 percent, a difference of 0.5 percent. In Android phones, those with slow charging degraded by 8.8 percent, and those with fast charging by 8.5 percent, a difference of 0.3 percent.

In the test where charging was only done between 30 and 80 percent, the detected degradation was lower: on iPhone, 4 percent capacity loss with fast charging, and 6 percent on Android, with a 2.5 percent difference between the two operating systems.

These tests led them to state that fast charging does not degrade the battery more than slow charging, and maintaining charge levels between 30 and 80 percent helps preserve quality but does not prevent complete degradation.

On the other hand, they conducted another test to demonstrate whether charging the battery to 100 percent also causes damage. Here, phones were divided into three groups: one left at 1 percent, another at 50 percent, and a last group with phones plugged in at 100 percent. After a week, no changes in battery capacity were detected.