Is Fast Charging Killing the Battery? A 2-Year Test on 40 Phones

Quick Overview

The two-year experiment on 40 phones conclusively demonstrates that fast charging does not cause significantly more battery degradation compared to slow charging, with the Fast-Charging Group losing 12.3% capacity versus 11.8% for the Slow-Charging Group after 500 cycles, and performance throttling only becomes noticeable when iPhone battery health drops below 85%.

Key Points: After 500 charge cycles, the Fast-Charging Group (using 120W charging) lost 12.3% of battery capacity, while the Slow-Charging Group (using 18W charging) lost 11.8%, showing minimal difference. The experiment involved groups of iPhones charged at 120W (Fast), 18W (Slow), 50% Fast Charging (80W-100W), and a Control Group (30%-80% range). Performance throttling (slowing down the device) only became significant when the iPhone battery health dropped to 85% or below, regardless of the charging method used. A separate test on Android phones showed the Slow-Charging Group lost 8.8% capacity, while the Fast-Charging Group lost 8.5% after 500 cycles, reinforcing the minimal impact of fast charging. Keeping the battery level between 30% and 80% offers limited protection against wear, and keeping a phone fully charged or nearly empty for extended periods causes almost no change in battery capacity over one week. In a separate performance test, the phone with 77% battery health shut down after 3 hours and 52 minutes of continuous heavy use, whereas a new battery lasted significantly longer.

Context: The video documents a long-term experiment conducted over two years, testing the impact of different charging speeds—specifically fast charging versus slow charging—on the long-term health and capacity of smartphone batteries, primarily focusing on various iPhone 12 models and some Android devices. The experiment aimed to verify common user beliefs that fast charging prematurely kills battery life.

Detailed Analysis

The video details a two-year experiment testing battery degradation across different charging methods on 40 phones, primarily iPhones, but also including Android devices. The main finding is that fast charging (using 120W chargers for the fast group) does not significantly damage battery health compared to slow charging (using 18W chargers). After 500 charge cycles, the Fast-Charging Group lost 12.3% capacity (starting at 3000mAh, ending at 2610mAh), while the Slow-Charging Group lost 11.8% capacity (ending at 2670mAh). A control group, charged only between 30% and 80%, showed the least degradation at 0.3% loss, confirming that limiting the charging range offers marginal benefits. Performance throttling, where the phone slows down due to battery issues, only occurred when iPhone battery health dropped below 85%. An Android subset test corroborated these findings, showing minimal capacity difference (8.5% loss for fast charging vs. 8.8% for slow charging). Furthermore, testing showed that keeping a phone fully charged or nearly empty for a week resulted in negligible capacity loss, contradicting the common belief that full charge cycles are essential for battery longevity. The video concludes that for current smartphone batteries, daily charging habits have a minimal impact compared to the inherent chemical aging process.