What “fast charging” really means in everyday use
Fast charging speed test results describe how quickly a phone or battery gains charge in real-world use compared with the maximum numbers promoted in marketing, taking into account charging curves, charger limits, and battery capacity over time. Phone makers highlight peak wattage figures – 40W, 60W, even 120W – but your phone does not sit at those speeds for most of its charge. Power ramps up, plateaus, then tapers off to protect the battery and avoid heat. That means a “120W” phone can spend much of its session pulling far less power. Independent testing, both on smartphones and power banks, shows why many people feel their devices fall short of the box claims. To judge true phone charging performance, you need to look at time to 50%, 80%, and 100% with real chargers, not only the headline watt figure.
How we tested phone and charger performance
To compare real charging vs advertised numbers, we looked at controlled tests of both power banks and phones. In ZDNET’s lab, power banks were charged from 0% to 100% through a 70W USB‑C adapter while a plug load logger tracked energy drawn from the wall every minute, then translated that into time to hit 50%, 80%, and 100%. For phones, a Mecheer power meter measured live wattage while charging a Samsung Galaxy S26 Ultra, iPhone 17 Pro Max, and OnePlus 15 twice: once with each brand’s own plug and cable, and once with an Anker Prime GaN charger and Anker USB‑C cable. This set-up turns the marketing claims into hard data, showing how long each device needs to go from empty to full, and whether third‑party accessories can match or beat the official bricks in a realistic fast charging speed test.
iPhone, Samsung and OnePlus: who matched the claims?
Looking at iPhone Samsung charging performance, the flagships did not behave the same way. The iPhone 17 Pro Max, rated for 40W wired charging, briefly exceeded that limit in its first five minutes on the cable before settling into a lower, safer range. Samsung’s Galaxy S26 Ultra, advertised at 60W, peaked at about 61W, showing that its real charging vs advertised numbers line up well. The most surprising result came from the OnePlus 15 and its bold 120W claim. In testing, the phone spent its entire charge window in the 20W–40W band and topped out at 46W on the OEM charger. That quote-worthy gap highlights the difference between ideal lab conditions and what a wall socket, cable, and battery management system allow in practice over a full charge session.
OEM vs Anker: when third-party chargers win
One major finding is that the charger you pick matters almost as much as the phone itself. Two of the three phones tested do not include a wall plug in the box, nudging buyers toward either an official adapter or a third‑party option. Using an Anker Prime GaN charger and Anker USB‑C cable, the tester saw both the Galaxy S26 Ultra and OnePlus 15 charge faster than they did with their own brand-name chargers. That is a clear example of how a reputable third‑party charger can improve real charging performance without changing the phone. By contrast, the iPhone 17 Pro Max behaved more predictably, staying close to its advertised ceiling no matter which compatible charger it used, though it still exceeded 40W briefly. The key is matching a modern GaN adapter to your phone’s supported standards.
Practical takeaways: choosing chargers and setting expectations
These tests echo what lab work on power banks has shown: raw wattage on the box rarely predicts full-charge time by itself. In one set of power bank tests, ZDNET’s lab crowned the Cuktech 15 Air the fastest to 100%, at 54 minutes, while another model hit 50% in a little over 13 minutes yet took more than three hours to finish. Phones behave the same way, front-loading charge speed and slowing down later. For buyers, the lesson is simple. First, look beyond peak watts to real timelines: how long does it take to hit 50% or 80% in independent tests? Second, consider a certified third‑party GaN charger from a known brand if your phone ships without a plug. Finally, expect that your device will feel fast in the first half hour, then gradually ease off to protect the battery, even if the marketing says 60W or 120W.
