This slim concept phone has a 15,000mAh battery, but one giant drawback

The advent of silicon-carbon batteries has resulted in many smartphone brands offering bigger batteries than ever before. We’ve already seen HONOR and vivo launch phones with ~8,000mAh batteries in relatively slim designs. Now, realme has revealed a rather impressive concept phone.

Realme has announced a concept phone with a 15,000mAh battery. We’ve seen rugged phones with larger batteries, but this typically comes with the side-effect of a thick, heavy design. However, realme manages to fit all this juice into a form factor that doesn’t look like a brick. In fact, the company claims the concept phone is only 8.89mm thick.

In other words, realme’s concept phone offers triple the battery capacity of the Samsung Galaxy S25 Ultra in a chassis that’s 0.7mm thicker. The company also claimed that this battery capacity was almost on par with the combined capacity of the iPhone 12, iPhone 13, iPhone 14, iPhone 15, and iPhone 16 (16,244mAh).

A 15,000mAh battery is larger than some power banks on the market, and realme indeed says you could use reverse wired charging to charge a drone, power a small refrigerator, and more. Otherwise, it says you can expect up to five days of typical usage, 50 hours of video playback, 30 hours of gaming, or three months’ standby time in flight mode.

There’s no word on the concept phone’s charging speed, but I imagine that even 120W wired charging would take a few hours. Then again, that seems like a small price to pay for a week of usage.

Unfortunately, realme hasn’t revealed any plans to deliver a commercial phone with a 15,000mAh battery. This was previously echoed by a leaker a few days ago. However, the same leaker said realme’s previously revealed 10,000mAh concept phone is ready for mass production.

There’s one major obstacle to making this 15,000mAh phone a reality. Realme confirmed during its fan event that it’s using a 100% silicon-anode battery in the device. Today’s silicon-carbon batteries only use silicon for a small portion of anodes (typically up to ~10%), while more traditional graphite is used for the rest. That’s because higher silicon content results in more expansion and greater degradation over time. So phone manufacturers choose batteries with low silicon content to mitigate safety and degradation concerns while still offering increased capacity.

In other words, a phone with a pure silicon battery like this realme concept device would be extremely prone to battery swelling and degradation. This suggests that we shouldn’t expect to see a commercial version of this 15,000mAh phone any time soon. It simply doesn’t appear to be safe for long-term usage.