In summary, there's good news for those worried that their battery might suffer from fast charging. The remaining battery capacity was virtually identical in the test groups using fast and slow charging, with a difference of less than 1 percent. However, the group that consistently charged between 30 and 80 percent proved to be more stable. Charging and discharging within this range is therefore more effective for the battery in real-world use, resulting in iPhones having 4 percent more capacity than those using full fast charging. For Android phones, the difference was 2.5 percent.