Xiaomi promises its 120W fast charger won’t kill its new phone’s battery

If you’ve been following the Chinese phone scene for the past few years, you’ll have noticed the inescapable fast-charging arms race. It feels like every few months there’s a new champion, with high-wattage chargers constantly pushing down the time it takes to fill a phone battery.

This month, Xiaomi is making its biggest effort yet to bring its “HyperCharge” technology to a mainstream, global audience. The upcoming Xiaomi 11T Pro has a 120W charger, a huge power increase on the current global flagship Mi 11, which uses a 55W charger that can get you to 100 percent in 45 minutes. Xiaomi hasn’t revealed estimating charging times for the 11T Pro yet, but last year’s China-only Mi 10 Ultra also had a 120W charger that took just 23 minutes to fill up.

A common reaction I see to this kind of fast charger is that they’ll surely have a negative impact on battery longevity, or that there must be safety issues, or both. So I talked to Daniel Desjarlais, international head of communications and global spokesperson at Xiaomi, about the company’s fast-charging technology efforts and what people outside China should expect from the 11T Pro.

First off, how does it work? “It’s like having two different inlets to fill the gas in your car and two separate tanks,” Desjarlais says of Xiaomi’s dual-cell battery design, which is similar to how other high-powered fast-charging solutions work. “Now, rather than filling at a certain slow rate on one side, you can fill up two at the same time. This is all done on the side of the phone, the charger outputs 120 watts and rather than trying to push the maximum of five volts, a single channel splits it into two, three, four channels. This allows us to increase everything — everything is done at 20 amperes.”

Desjarlais went on in detail to explain what happens with the technology in the battery itself, and how Xiaomi’s thermal monitoring systems work to maintain the optimum charging speed at each point in the cycle, but as a non-engineer I’m frankly not qualified to comment on the electrical design here. What I am qualified to comment on is phone design and consumer expectations, and I know a lot of people do worry about the tradeoffs with these fast-charging systems.

On the question of longevity, Desjarlais says you can expect endurance in line with other more conventional phones. “This is something that we’ve really, really heavily tested,” he says. “Generally, for this level of charging with the batteries that we’ve tested it with, after 800 charging cycles you’ll still have 80 percent battery health. Now, that 20 percent might sound like ‘oh wow, I’m losing 20 percent,’ but that’s quite standard across basically all charging tech. 800 cycles, for most people, it’s going to be two years roughly. So that’s quite solid.”

For comparison, Apple — a company that has faced heavy scrutiny over its long-term battery performance while offering slower charging tech than most of its competitors — tells customers to expect a lithium-ion battery to retain “up to 80 percent of its original capacity at 500 complete charge cycles.” If Xiaomi’s testing figures are accurate, a phone like the 11T Pro shouldn’t suffer from an unusually short lifespan, even if its owner only ever uses the fast charger.

When I ask whether using slower chargers would improve battery health further, Desjarlais says “There’s relatively minute differences between the two. Of course, the optimal situation would be yes, to use the slower charger if you’re going to charge overnight and use the fast charger for more rushed situations.” But Xiaomi’s testing has been carried out with the presumption that you could get good battery health if you use fast charging all the time.

As for safety, Desjarlais says the testing has been extremely thorough and includes third parties, with 34 different battery protection features included in the device itself. “Generally this is part of the reason why this technology is coming out now for global markets,” he says. “We wanted to make sure that we met all the regulations, but also that it was incredibly safe for all.”

Still, I wondered about those potential tradeoffs. Are there really no downsides to a charging system like this? Could a phone with more conventional charging be thinner, or house a bigger battery, for example? According to Desjarlais, there’s no negative impact. That said, the actual charger is quite a bit larger than the average phone pack-in, and will of course draw more power (albeit for shorter periods of time.)

Xiaomi thinks its fast-charging technology is here to stay, and there still could be room for improvement. Earlier this year, for example, the company demonstrated a prototype 200W system that filled a 4,000mAh battery in 8 minutes, though Desjarlais would only say that “Whether or not this comes [in a commercial product] is something that you’re going to have to wait and see on,” citing the need for further safety and performance testing. He had much the same answer about Xiaomi’s truly wireless Air Charge teaser, saying “It’s a wonderful concept and it’s something that we’re continuing to examine.”

Obviously, safety and effective performance should be the least you expect out of any given phone feature. With fast charging, the question is whether customers in Xiaomi’s global markets will consider it a selling point. “For us, I think the big goal here is there’s a lot of people out there who consider fast charging to be an extraneous feature,” Desjarlais says. “But there’s also a lot of people out there for whom this is a big value add. It’s something you don’t really realize how good it is for your day-to-day life until you have to rush out the door to catch a cab in five minutes and your phone isn’t really charged.”

Xiaomi’s international launch event for the 11T Pro and the rest of the 11T series is taking place next week on Wednesday, September 15th.