Samsung is trying to build interest in the Galaxy S25 Edge by showcasing it behind glass enclosures at tech conferences ahead of its planned launch sometime in Q2 2025, but Chinese manufacturer Tecno managed to steal its thunder at MWC 2025 with the Spark Slim, currently the thinnest phone in the world.
The Spark Slim has a thickness of just 5.75mm, making it considerably thinner than Samsung’s upcoming ultra-thin phone. But where it truly stands out is the battery; Tecno somehow managed to slot in a sizable 5200mAh battery into the phone, and that’s just wild.
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I managed to get my hands on the device on the MWC show floor, and the sleek profile is a definite differentiator; it makes all other devices look bloated — particularly the Xiaomi 15 Ultra that I used to take these photos.
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The distinctive design feature is the camera island at the back, and the wide camera bar evokes memories of Motorola’s Droid devices of yesteryear. I really like the design of the camera housing, and while it protrudes slightly from the chassis, it isn’t all that noticeable. There’s an LED light ring around each module, and a horizontal bar that runs along the width of the camera housing, and it’s just plain cool.
Unlike most phones today, the Spark Slim has dual-curved edges on either side of the screen, and it has a curved sides where the back meets the mid-frame. This allowed Tecno to reduce the thickness even more, and while there isn’t much to hold on to at the sides — it measures 5.75mm, after all — it wasn’t uncomfortable to hold.
If anything, the plastic back and curved design assist in usability, and while I used plenty of ultra-thin phones in the past, the Spark Slim is notable because of its sheer battery size. It has a definite advantage over the Galaxy S25 Edge in that regard, and again, it’s somehow thinner than Samsung’s device.
The Spark Slim has a 6.78-inch AMOLED that goes up to 144Hz, and there are two 50MP cameras at the back and a 13MP camera located up front. Tecno didn’t reveal the internals, only stating that it is powered by an octa-core platform. The interface felt fluid in the 10 minutes I used the device, but then again, it was a demo unit and didn’t have anything installed.
At this point, there’s no mention of when (or if) the Spark Slim will make its debut. While it is a remarkable technical showcase, it isn’t clear at this point if Tecno will put the device into production, or if it can do so at scale while still retaining the ultra-thin design and the 5200mAh battery. Still, the Spark Slim is proof that it is possible to create a sleek phone with a huge battery, and I want Tecno to launch this device at some point — we need better alternatives to the Galaxy S25 Edge.