There have been various theories for years about how slow or fast charging affects our iPhone battery. And we finally have experimental data on the matter: HTX Studio has shown the results of a six-month test in which iPhone 12 models were charged slowly and quickly to compare the effects on the battery. The results are encouraging.
The experiment: 500 cycles and two charging methods
The YouTube channel set up six iPhone 12 units to charge and discharge continuously in a loop from 5% to 100%: three with fast charging and three with slow charging. In a parallel test, another group of iPhones was treated the same way but always kept between 30% and 80% battery.
Before continuing, what is a cycle? A charge cycle is the total of 100% worth of energy charged and discharged, regardless of how it is distributed. If in one day we use 40% and the next day 60%, we will have completed a full cycle even if we never went from 0% to 100% in one go.
The testers measured the actual capacity of each battery before and after completing 500 cycles over six months. For us as users, in normal iPhone usage with daily tasks and partial recharges, those 500 cycles usually represent a little more than two years.
Does fast charging damage the iPhone battery?
And the results? The extra health loss from using fast charging was minimal compared with slow charging. In other words, if from time to time we need to plug in the iPhone for 15 minutes and rush out with as much charge as possible, we can do so without worry. The device’s control system will take care of filling the battery without practically affecting its lifespan.
In addition, another test with iPhone 12 units stored at different battery levels showed that leaving a device at 1%, 50% or 100% while it remains powered off for a week does not cause any notable loss of capacity. This tells us that real battery ageing appears in the long term and is tied to the passing of time, temperature and repeated charge cycles, not to a specific energy level for a single week.
Moreover, the idea that keeping a phone at full charge for a relatively short period accelerates degradation is not entirely accurate according to this test.
And what about the famous 30–80%?
As a MacRumors editor also confirmed, it is true that always keeping the charge between 30% and 80% showed a very slight advantage, but the benefit was minimal (only around 4%). So, if this charging style fits into our daily routine, great. But if not, we are not going to harm the battery more by charging to 100% when we need it.
Therefore, the conclusion of this test is that we can charge our iPhones in whatever way works best for our usage and needs. The extra impact of fast charging is minimal. That said, it is always worth keeping in mind certain aspects such as avoiding unnecessary heat, enabling battery optimisation and other tips that will help keep our iPhone battery in great condition after years of use. After all, being able to enjoy our iPhone is what matters most.
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