There’s some controversy surrounding fast charging an Android smartphone, specifically whether the ultra-quick technology that tops it up within a few minutes is bad for the battery's lifespan. There have been many stories of early failure and some cases of overheating, fire, and explosions. More important than concerns about the device, there’s a question about the safety of being near an Android phone that’s absorbing energy at such a high charging rate.
When smartphones first appeared in the market, the greater demands placed on their batteries caused runtime to be shorter than was ideal. It wasn’t uncommon for a phone's battery to run low within hours. Charging was also a burdensome task compared to modern smartphones where batteries can give users hours of use with just minutes on the charger. For early smartphones this problem was solved by using removable batteries, allowing ongoing use simply by swapping out charged batteries. For better or worse, those days are over and smartphone batteries are no longer user-replaceable.
Fast charging really shouldn't ruin an Android phone's battery even when manufacturers push the power supplied to over 100W. This is not to say the early demise of a smartphone due to battery problems can't happen. The truth is that the charging rate isn't really the problem, but rather the heat that might be generated as a result of the rapid flow of energy. Manufacturers like OPPO, Xiaomi, and others take great care in implementing cooling systems to help prevent problems with fast charging. Sensors detect rapid build-up and slow the charging rate when needed.
Beyond cooling systems and throttling the charge rate, there are design strategies that can help, such as dividing a smartphone's battery into multiple cells to lower the amount of power flowing in and heat generated while keeping an overall high charging speed. This also provides the flexibility needed for foldable phones like Samsung's Galaxy Z Fold 3, which has a battery on each side of the device. Putting more of the heat-generating electronics in the power adapter rather than the phone also helps. Despite these efforts, most smartphone manufacturers aim for a phone to retain only about 80 percent of its battery life after two years of use.
Individual habits might actually have a larger impact on battery life than charging degradation. The overall age of the smartphone and how many times the battery has been cycled between charged and discharged affects the maximum charge level. Setting screen brightness to the maximum level drains the battery faster and requires charging more often. Keeping a lithium battery fully charged or completely drained also shortens its life. There are many factors that affect the battery capacity of an Android smartphone and fast charging does not deserve the degree of skepticism it's often met with.
Source: OPPO, Xiaomi/Twitter
