Capacity is not endurance
Rated capacity, measured in milliamp-hours, is the starting point rather than the answer. The OnePlus 13 and Xiaomi 15 Ultra both ship with 6,000 mAh cells, the Galaxy S25 Ultra with 5,000 mAh, the Pixel 9 Pro with 4,700 mAh and the Fairphone 5 with 4,200 mAh. Yet endurance depends equally on chip efficiency, panel type and software tuning. A phone with a smaller cell and a very efficient processor can outlast a larger one with a power-hungry chip. Look for independent tests, such as the PCMark Work 3.0 battery benchmark or the active-use scores published by review sites, before drawing conclusions from the capacity figure.
Charging speed and what it costs
The OnePlus 13 charges at up to 100 W by cable and 50 W wirelessly. The Xiaomi 15 Ultra manages 90 W wired and 80 W wireless. The Galaxy S25 Ultra settles at 45 W wired, while the Pixel 9 Pro charges at roughly 27 W wired and 21 W wirelessly with Google's own stand. The Fairphone 5 charges at 30 W by cable and has no wireless charging. Faster charging saves minutes, but sustained heat ages a lithium cell, so look for features such as an 80 or 85 percent charge limit and adaptive overnight charging. Samsung, Apple and Google all offer some version of this.
Cycle life and the EU rules
A full charge cycle means using 100 percent of capacity, which may be spread across several days. Since 20 June 2025, the EU ecodesign rules for smartphones require that a battery retain at least 80 percent of its capacity after 800 full cycles, and that makers provide operating system updates for at least five years after a model leaves sale. Phones also need a minimum ingress rating and a clear repairability and energy label. Even outside the EU, global products tend to follow these standards, which is good news for buyers everywhere.
Updates, repairs and resale
Longevity is a package. Samsung and Google promise seven years of updates on the S25 Ultra and Pixel 9 Pro, while OnePlus promises four Android versions and six years of security on the OnePlus 13. Fairphone commits to software support to at least 2031 for the Fairphone 5, and it sells a battery you can swap in minutes with no tools. Repairability also protects resale value, because a phone with an affordable battery replacement is easier to keep and to sell on.
Habits that add years
Avoid leaving the phone at 100 percent charge for long periods, keep it out of hot cars, and use a mid-range charger rather than the fastest one when you charge overnight. A fresh battery replacement at year three often does more for daily comfort than a new phone.