Do fast-charging phones still harm battery health? I tested them to find out

Fast-charging technology has been around for many years now, morphing through many forms across the best smartphones of the last decade. Chinese brands have long led the way in terms of power and speed, evolving from once ground-breaking 40W capabilities in HUAWEI’s early SuperCharge models to over 100W via HyperCharge and other standards. While faster charging times have been a boon for us power users, ever-higher power levels have rightly led many to be skeptical of the effects on long-term battery health.

Smartphone batteries are finicky bits of kit. They dislike extremely high temperatures and require very careful voltage calibration as they reach full charge, something fast charging technologies have sometimes pushed right to the limit in the pursuit of ever-quicker charge times. Annecodaily, a couple of friends have felt the sting of this double-edged sword, with once fast-to-charge HUAWEI and OnePlus flagships struggling to make it through a full day anymore. Their batteries prematurely aged after just two or three years of use.

In recent years, those once-distant promises of 500, 800, or even 1,200 charge cycles before batteries start degrading have been coming home to roost. Leaving a few of us to regret leaving our phones to charge on an extra-speedy adapter.

Thankfully, things change. Brands and consumers are more aware of long-term battery health than ever before, prompting Apple, Google, and others to offer optimized overnight charging features, bypass charging capabilities, and battery health statistics. Fast charging capabilities themselves appear to be taking a more conservative approach in the past twelve months, with some brands even requiring users to manually toggle a temporary boost for the fastest possible charge time.

I’ve been testing and tracking smartphone charging capabilities for years now and have noticed something else quite interesting this year: Chinese brands, in particular, are now besting some of the Western household names not just in terms of power and charge times but also in terms of lower peak and average battery temperatures. Looking at the table below, temperatures below 40°C are OK, with 35°C or below being ideal for ensuring batteries don’t lose their peak capacity due to added heat stress.

The OnePlus 13 is by far the most impressive phone I’ve tested this year. Not only is it one of the fastest phones to charge by maintaining higher average power than most of its competitors, but it’s also far cooler than every other phone on our list by about 10%. It’ll charge quickly and won’t see its battery capacity drop unduly early.

To its credit, Samsung’s Galaxy S25 Ultra is one of this generation’s better phones for charging. It, too, maintains low temperatures and decently quick charge times, along with the OPPO Find X8 Pro, which also sits in that ~35°C sweet spot for charging temperatures. I highly recommend all three of these phones for those who want a fast-charging phone with minimal risk to long-term battery health.

The vivo X200 Pro isn’t too far off the pace either, with peak and average temperatures just slightly higher than I’d prefer but still far enough below our warning level to not cause concern. Its peak and average power levels are also equally robust, allowing the phone to reach full in just over 30 minutes.

Xiaomi 15 Ultra is a little closer to our warning level and actual prevents itself from going over, hence why it doesn’t sustain its claimed high power rating for very long at all. The HONOR Magic 7 Pro is faster to charge and runs at virtually the same temperatures, suggesting it has the slightly better implementation. However, 40°C is the upper limit acceptable peak temperature for long-term battery health, so there is a chance these phones might see some additional battery wear over many fast-charge cycles. Even so, given fast charging’s history of blitzing through battery life, all five of these big Chinese brands are now balancing speed with longevity. At least where their ultra-premium flagships are concerned.

At this point, I’m a little more worried about the remaining phones on my list. ASUS’ Zenfone 12 Ultra is at least nippy to charge, but it scores the highest average temperature on our list, meaning a longer heat exposure time for the battery that’s likely to decrease its remaining capacity quicker than the rest.

This leaves Google’s Pixel 9 Pro and Pixel 9 Pro XL as the worst of the bunch. They’re sluggish to charge, but we already knew that. What’s more worrisome is that they also have higher maximum temperatures than all of the fast-charging Chinese phones I’ve looked at this year, with 9-10°C worth of extra heat compared to the leading OnePlus 13. Average temperatures are more in line with the rest, but given the much longer charge times, this still amounts to additional prolonged exposure to non-idle temperatures than the rest of our test subjects.

Temperatures aren’t the whole picture. Stress is also applied to batteries when fast charging near full capacity, and we know that Apple and Google are particularly cautious in this regard. Equally, picking a battery with the ideal C-rating (its ability to handle high currents) is an important factor in determining how much heat is generated/wasted during charging (running close to the C-rating increases internal resistance and, therefore, heat), as does the efficiency of the phone’s USB charging circuitry. But that’s beyond the scope of our data; all we do know is that many of the better-performing phones are based on newer silicon-carbon Li-ion batteries. In any case, higher temperatures suggest more power being wasted, which in turn heats the battery, contributing to a reduced lifespan.

Undoubtedly, the push for four, five, and even seven years of software update support has forced brands to reconsider the pros and cons of fast charging, and this is reflected in a much more level playing field for charging temperatures than a few years ago. Thankfully, the quickest phones can keep peak temperatures below or even cap them at 40°C and, in some cases, much lower. Impressively, China’s top brands maintain a high level of power, at least temporarily, although we appear to have reached the limits of what can be achieved without too great a hit to battery longevity.

When paired with battery-preserving software features like 80% charging limits, adaptive overnight charging, and the greater use of user controls to only supply fast charging when required, I’d say the days of being worried about Chinese phones needing an early battery replacement are mostly in the past. Of course, there are differences across my results, and some Chinese brands are certainly better than others. However, I’m a bit more concerned about how long the latest Pixels will last before needing a battery replacement than I am with the OnePlus 13, something I definitely didn’t think I’d ever say just a few years ago.