Forget iPhone 17 Air, Tecno Spark Slim Is A Stupid Thin Phone With A Big Battery

Tecno Spark Slim smartphone being held by fingers on a gray background.
Seeing smartphone makers trip over themselves in a suddenly emerging race to claim the title of world’s thinnest handset reminds us of the classic Saturday Night Live skit, the one where Will Ferrell pulls out a ridiculously tiny flip phone, much to the glee of Jimmy Fallon and guest host Sean Hayes, both of which broke character with laughter at the silliness of it all. We’re not quite there yet in real life, but there is a push for increasingly slimmer profiles. As such, meet Tecno and its Spark Slim prototype.

Tecno shared a handful of images on X/Twitter that highlight the extreme thinness of the Spark Slim, the timing of which comes just ahead of this year’s Mobile World Congress (MWC) event. In the post, Tecno anoints the Spark Slim as the “world’s slimmest” smartphone to boast at least a 5,200mAh battery pack, with a profile that measures a scant 5.75mm.

To put that into perspective, Samsung’s Galaxy S25 Ultra measures 8.2mm thick, Google’s Pixel 9 Pro XL has an 8.5mm waistline, and in the world of iOS, Apple’s latest generation iPhone 16 Pro Max is 8.25mm wide. Of course, there are thinner variants, sometimes even within the same product lines. For example, the regular iPhone 16 measures 7.8mm, which is pretty thin in a vacuum.

It should also be noted that within the realm of foldables, there are even thinner slabs. One example is Oppo’s Find N5, which is 8.9mm when folded but just 4.2mm when unfolded.

As shown, Tecno’s Spark Slim is conceived in the traditional smartphone form factor (read: not a foldable or a flip phone). Should it come to fruition, it would be an impressive feat to cram a 5,200mAh battery inside a svelte phone that measures a mere 5.75mm thin. We’re assuming that measurement doesn’t take into account the camera on the rear.

Other specs include a 6.78-inch curved OLED display and dual 50-megapixel cameras. It’s not clear what kind of chipset it might be equipped with, and at this level of thinness, thermals, cooling, and the potential for faster throttling become obvious points of concern.

In any event, it will be interesting to see if the Spark Slim becomes an actual product, and if so, how it will compare to upcoming competitors, including the Apple’s iPhone 17 Air and Samsung’s Galaxy S25 Slim. As for those specific handsets, the former is rumored to be 5.5mm while the latter is said to be 5.6mm. It’s not yet known what kind of battery capacities those handsets will have when they launch.

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