Find Out If Fast Charging Is Bad for Your Smartphone

A decade ago, most of us were frustrated on a daily basis by the amount of time it took to charge our smartphones. Manufacturers recognized that frustration and began to introduce various types of fast charging and rapid charging technologies. Today, you might be able to go from zero to almost a full charge in about an hour, depending on your phone model and the charger. But that may make you wonder if you're damaging your phone's battery. To find out if it does, GreatScott! built a charge and discharge testing rig.

There is good reason to be concerned about fast charging. If that doesn't harm the battery, then why didn't smartphone manufacturers take advantage of it from the beginning? The battery chemistry (Lithium-Ion) is the same and it would have been trivial to build compact chargers that output enough current several decades ago. The answer might be in the charging methodology, with modern fast chargers taking care to output power in a way that avoids damage. GreatScott! wanted a concrete answer based on real experiments, he just needed a way to charge and discharge a bunch of batteries many times.

GreatScott! wanted to perform 100 discharge/charge cycles for each of the six test batteries. People tend to charge their smartphones every night, so that simulated about 100 days of typical use. To perform the test in a reasonable amount of time, GreatScott! built six charging stations. An Arduino Nano development board controls each of those through a custom PCB, with a small OLED screen showing the voltage and number of charge cycles at any given time. The discharge circuit draws exactly 1A of current through an op-amp any time it is active, converting the battery's electricity into waste heat.

The results were interesting. The batteries charged at the standard 1A of current had negligible degradation that fell within a reasonable margin of error. But the batteries fast charged at 5A showed a noticeable decrease in capacity. They lost an average of 1.6% capacity over those 100 cycles. That might not sound like much, but it would become significant over the course of a couple of years if the rate of capacity loss remained constant. And GreatScott! suspects that the rate would actually increase, which would make the problem much more severe.

We'd like to see more tests to determine how the rate of capacity loss changes. However, it is already reasonable to conclude that you should avoid fast charging when possible if you want to extend the life of your smartphone battery.