Kuxiu S4 25W Semi-Solid Wireless 10K Power Bank review: thinnest 10K magnetic power bank

Best Prices Today: Kuxiu S4 Semi-Solid Safe 25W Wireless 10K Power Bank

When we reviewed the Kuxiu S3 25W 10K Solid-State Power Bank we called it the “fast 25W wireless battery pack that has it all”. We were impressed by its built-in USB-C cable, integrated kickstand, and super-clear digital battery display.

Now, the same company has released the S4 Power Bank. It’s not the S3 plus some more. In fact it’s a bit less than the S3, but in one aspect that’s great news—because the Kuxiu S4 is the slimmest 10K magnetic wireless power bank we’ve ever tested. And it’s pretty special in other ways, too.

Power bank specs

• Capacity: 38.5Wh (10000mAh)
• Input charger: USB-C (30W)
• Output charger: Wireless (25W) & USB-C (30W)
• On test charged iPhone to: 182%
• Weight: 7.55oz (214g)
• Dimensions: 4.1 x 2.7 x 0.53 inches (104 x 69 x 13.7mm)
• Colors: Cosmic Orange, Black

Battery capacity: 10000mAh (10K) is the largest battery size that you can clamp to the back of your MagSafe iPhone without it being too cumbersome to pocket—and small pockets will better appreciate a 5000mAh (5K) power bank. Read reviews of all the best magnetic power banks we have tested, both 5K and 10K.

Not all 10K or 5K power banks have exactly the same capacity. To get more precise you need to look at the capacity in watt hours (Wh). The S4’s 38.5Wh is a smidge under the S3’s 39.5Wh. The average 10K battery capacity in watt hours is 37.9Wh.

Speed: For power output the S4 is rated at the top 25W, using the latest Qi2.2 wireless charging technology. Only the iPhone 16 series and later can take all 25W, with older iPhones pegged back at 15W (still much faster than still-available 7.5W battery packs). Note that the 17e is also limited to 15W, and the iPhone Air to 20W.

In our tests the S4 recharged our test iPhone 16 Pro to 50% in 32 minutes, which is what we’d expect from a 25W charger, and much faster than the average 45 minutes it would take with a 15W wireless charger.

The S4’s USB-C port is rated at 30W so will charge your iPhone faster if you need to power up as quickly as possible, but you’ll need to bring a USB-C cable—unlike with the S3 that comes with its own built-in. The very fastest wired iPhone charging we’ve seen from a magnetic power bank is 45W from The Baseus PicoGo AM52, but it’s unlikely the iPhone will accept much more than 35W anyway.

When recharging the S4 power bank, the power input is 30W—at the top end of magnetic wireless power bank range.

Like the S3, the S4 is built using semi-solid-state (SSS) battery technology that’s engineered for superior safety, longevity and thermal stability compared to standard lithium-ion battery packs. You can skip the next bit if you’re not interested in technical details…

What are Semi-Solid State batteries?

Semi-Solid is a transition technology between traditional liquid lithium-ion batteries and all-solid-state batteries (ASSBs). When all solid-state batteries are mainstream, they will likely replace semi, but semi is as good as we have today. Once proven in electric vehicles, we expect to see ASSB power banks in by 2028.

Why so long? All-solid-state batteries will require new manufacturing facilities, while semi-solid-state batteries are compatible with existing lithium-ion production lines, requiring only minimal (10-20%) new equipment. As such, ASSBs will be expensive—maybe 3-4x—than traditional batteries and so are unlikely to be seen in mainstream laptops until manufacturing ramps up and costs go down..

SSS batteries replace a large portion of flammable liquid electrolyte with a gel or slurry, typically only 5–10% liquid remains. The reduction of flammable liquid significantly lowers the risks of thermal runaway, leakage, and fire. They are more resistant to extreme heat and physical damage. This is why we expect airlines to allow only solid-state batteries on flights in the future. This improved thermal stability also means the batteries should perform better in colder temperatures.

Aside from greater safety, solid-state tech allows the battery to have a higher energy density, so they can be made smaller. They should also last longer with a greater number of possible charge cycles before capacity degradation.

Thinnest design yet

Kuxiu calls the aluminum-alloy S4 “the world’s thinnest 10,000mAh semi-solid-state cell”, and it’s not wrong.

13.7mm is the thinnest 10K power bank we’ve tested. The previous champ, the Anker MagGo 10K Slim, is a full millimeter thicker and offers only 15W power output. The average depth of a 10K power bank is 18.2mm.

Some other 10K power banks are 16mm or 17mm deep, but the average is 20-22mm. The S4 is a third thinner than those chunky beasts. Let’s be honest, it’s not a sliver of a power bank—it still looks large compared to the thinnest 5K battery packs—but it is the slimmest 10K.

Even the 5K power banks we’ve tested average out at 10.7mm depth, although the slimmest of all (the BMX SolidSafe Air 5K) is a mere 6.8mm deep.

Kuxiu S4 vs Kuxiu S3: slim vs cable

The S4 is noticeably slimmer than the S3 but lacks its long integrated USB-C cable. That means Kuxiu has been able to make the S4 over 35% slimmer—14mm vs 22cm.

While we love a built-in cable on a magnetic power bank (wired charging is always faster and a cable makes recharging the power bank itself less hassle), we also desire them to be as slim as can be.

That’s the major compromise between choosing between the S3 and S4, but there are more differences. Read our Kuxiu S3 review for more details.

Both power banks feature a stand, and the S3’s stand is larger and more robust than the S4’s bottom-mounted pull-out but the S4’s performs well enough.

Both have a digital display so you can see precisely how much power remains in the power bank—most make do with four tiny LEDs, each of which represents 25% battery charge, compared to the exact number a digital display readout gives you.

The S3’s is clear to read but shows just the remaining battery charge. The TFT display on the S4—tucked behind the stand—is smarter and more colorful, showing battery health, operating temperature, battery level (remaining charge), wireless charging power and USB-C input/output power plus battery safety alerts where appropriate.

You might not need to know all that info but it’s there, presented on three digital circles.

Finally, the Kuxiu S4 is available in a stunning Cosmic Orange to match the iPhone 17 Pro and Pro Max as well as the same Black as the S3.

Recharging performance

At Macworld we produce a battery performance report for all the power banks that pass through our labs.

There’s nothing fancy involving microscopes and spectrometers. We simply drain an iPhone’s battery to 0%, connect the power bank and see how many times it can recharge the phone. If it fills the phone up with juice to spare, we wait till the phone has run out again and repeat until the power bank is empty.

The best score we have got from a 10000mAh (10K) power bank is 190% (the 15W EcoFlow RAPID 10K), with an average score of 166%. The Kuxiu S4 scored an impressive and above-average 182%—around the same ballpark as the S3.

Price

The Kuxiu S4 10K Magnetic Power Bank is priced at $84.99 or £64. The S3 is cheaper at $68.99/£54, even with its integrated cable.

If you want the thinnest 10K magnetic power bank, you’ll need to dig a bit deeper, but your trouser-pocket lining may thank you for it over the long term.

For more options we have tested and reviewed the best magnetic wireless power banks.

Should you buy the Kuxiu S4 25W Wireless 10K Power Bank?

First things first: the Kuxiu S4 is the slimmest 10K magnetic wireless power bank we have tested yet. If you want thinner, you’ll have to sacrifice half the battery capacity with a 5K battery pack. The S4 performed above average in our recharging tests. If you can sacrifice the slimness, consider its S3 sibling that boasts an integrated USB-C cable, but we salute the S4 for being the slim semi-solid-state champion… and we love the Cosmic Orange option.

Best Prices Today: Kuxiu S4 Semi-Solid Safe 25W Wireless 10K Power Bank