Tecno Spark Slim Wants To Be The World's Thinnest Phone, And With A Bigger Battery Than Galaxy S25 Ultra

It seems the trend of 2025 is going to be around slimmer smartphones, and Tecno wants to set the record with its new “Spark Slim” which, if it ships, could hold the title of “world’s thinnest phone,” at least for a little while.

The Tecno Spark Slim is being shown off at MWC 2025 next week and, ahead of that, the company is revealing two key specs around the ultra-thin smartphone. First and foremost, the Tecno Spark Slim aims to capture the title of “world’s thinnest smartphone” by delivering a mere 5.75mm profile. For context, that’s over 33% thinner than the Galaxy S25 Ultra, and also nearly 2mm thinner than the iPhone 16.

It’s unclear how long that title would last, though. Samsung won’t beat it, as the upcoming Galaxy S25 Edge is said to be 5.84mm thick. Apple, though, might push things further with the iPhone 17 “Air,” which is rumored to be as slim as 5.5mm at its thinnest point.

In any case, it’s an impressive feat, but what’s more impressive is the battery capacity.

Tecno says that the Spark Slim would contain a 5,200 mAh battery.

That’s a battery 200 mAh bigger than the 5,000 mAh one in the Galaxy S25 Ultra, for a phone that’s over 33% thinner. The likely explanation for how that’s possible is the use of silicone-carbon battery tech, which brands such as OnePlus/Oppo have been using to stuff 6,000 mAh batteries into “normal” smartphones like the OnePlus 13.

The huge catch on all of this is that the Spark Slim is, for now, just a concept from Tecno. The company is showing the device off in real life at MWC in Barcelona, but there are no firm plans to release the device yet.

In a statement, Tecno says:

TECNO is also showcasing a range of boundary-pushing concept devices, advanced technologies and revolutionary materials. This includes the SPARK Slim ultra-thin concept smartphone, a breakthrough concept creating the industry’s slimmest device with a 5000mAh+ battery. This technology ensures sleekness without compromising on powerful performance and is set to lead the way in the next wave of ultra-thin smartphone design

Tecno has been showing off concept devices for a long time now – including a rollable this time last year – and a lot of them have yet to ship. Will this one be any different? It’ll be interesting, to say the least.