KUXIU S4 Solid-State Power Bank: A Premium Product In Every Way

With all the talk lately about lithium-ion battery fires, especially on planes, it’s no surprise that manufacturers have started looking at alternatives.

So-called “semi solid-state” power banks use a different chemistry that replaces most of the liquid electrolyte inside the battery cells with a gel. This in turn means a much lower chance of catching fire if the battery gets punctured, damaged, or otherwise malfunctions. So that’s a good thing.

It’s early days for this technology, though, and not many companies have real products on the market yet. One of the exceptions is KUXIU, a company that’s been making innovative power banks for a few years now.

Their latest effort is the S4, a slimline 10,000mAh MagSafe-compatible power bank with a raft of features that would have made me interested to take a look at it even if it didn’t have that whole solid-state thing going on.

This is that look.

Design

The S4 is clearly intended to be a high-end product, and that even extends to the cable it comes with. It’s an attractive white, braided USB C version that looks like the kind of thing Apple should be including with its iPhones.

The casing is an aluminium alloy that feels great in the hand and helps dissipate the heat, with more rounded edges than usual. I like the sparse design of the wireless ring on the top of the S4, although all the logos, specs, and branding on the other edges do detract from the minimalist vibe a bit.

It’s on the back, however, where things get interesting. That’s where you’ll find a small fold-out kickstand that lets you prop up your Magsafe-compatible phone so you can watch a show and wirelessly charge at the same time.

There’s also a pill-shaped glass display at the bottom, visible through a large cut-out in the stand. That’s an information screen that provides all sorts of detail about what’s going on with the power bank, some of it useful, some of it perhaps less so. More on that below.

The S4 comes in two colors, the matte black model that I got and a vibrant orange version that matches the “Cosmic Orange” variants of the iPhone 17 Pro. It’s an attractive colour, and on a more practical note, makes the power bank easier to find when you drop it under your seat.

KUXIU’s marketing makes a lot of how slim it is, calling it “the world’s thinnest 10,000mAh semi-solid-state cell”. It’s not a crowded field.

Thing is, while it is relatively thin (although not quite as thin as some of the non solid-state 10,000mAh power banks I’ve got lying around), it’s still quite chunky when hanging off the back of your phone.

I tend to think that 5000mAh power banks are the sweet spot for size versus usefulness when it comes to MagSafe charging, at least if you’re planning to hold the phone and battery combo in your hand or stick it in your pocket.

If you’re using it on the stand or lying on a table, of course, it makes no difference at all. Just something to think about.

Features

The S4 gives you two charging options, USB C at up to 30W or Qi2.2 wireless charging at up to 25W.

Getting those maximum rates depends on your device: most mid to high-end phones of the last few years support 30W wired charging, but only a smaller number have support for Qi2. If yours isn’t one of them, you’ll still be able to charge wirelessly, but it’ll be noticeably slower.

The kickstand sits near one of the short edges and folds out to a 70-degree angle, which means the S4 sits comfortably in either portrait or landscape mode. The stand is lightweight and feels like it could be a bit flimsy, but so far so good on that front: even with a phone attached, it hasn’t toppled over yet.

The colourful display on the back cycles through all kinds of information, some of which is useful, some of which may not be. Along with the remaining capacity, you can see the wired and wireless power output, internal temperature, and overall battery health.

There’s also a safety alert, which flashes and beeps to let you know the power bank has got too hot. You can test this out by repeatedly pressing the power button.

Speaking of safety, as I mentioned up top, the use of semi solid-state technology should mean there’s far less chance of thermal runaway if this thing gets damaged. Think “a small puff of smoke” rather than “a blazing fire that’s very hard to put out”.

That’s genuinely great, and I’m absolutely here for it. The only problem right now is that it won’t make any difference to your ability to put it in your checked bag or use it in the cabin if that’s something your airline prohibits for normal lithium-ion batteries.

Debating the finer points of battery chemistry with cabin attendants or baggage handlers is a battle you’re not going to win. For now, at least, you’ll almost certainly need to treat it like any other power bank if you plan to take it on a plane.

Specifications

Testing

Wireless Charging

I tested the wireless charging with a few different devices, starting with a Samsung Galaxy S24+ that only supports slower first-gen Qi. Unsurprisingly, while it worked as well as any other wireless charger I use with this phone, it’s slow.

Moving onto an iPhone 15 Pro and a Samsung Galaxy S26 Ultra, the difference was stark. Both support Qi2 and MagSafe (the iPhone natively, the Galaxy via a magnetic case), and charging rates jumped dramatically.

In each case I fully charged the S4 and drained the phone down to between 10 and 30%. From there I measured how long it took to add 50% charge, how much capacity was left in the power bank afterwards, and the highest power output I saw along the way.

Note that the power output is what was reported on the S4’s display screen, so it’s how much the power bank was putting out, not how much the phone was taking in.

There’s always quite a bit of loss with wireless charging: that’s particularly obvious with the iPhone 15 Pro in the table below, since despite that 20W number, it can’t actually charge wirelessly at more than 15W.

The magnets were nice and strong, with all of the various MagSafe-compatible devices I tested clamping firmly into place and not moving even with some pretty vigorous shaking.

Usefully, even though it’s not mentioned in the manual, the S4 supports pass-through charging. This means you can wirelessly charge a phone or other device while the power bank itself is charging from the USB C port.

The power bank charged more slowly, as you’d expect, but there was nowhere near as much difference as most other models I’ve tested. Input power dropped from 29W to 19W when wireless charging started; in other words, expect the S4 to charge at about 2/3 of its usual speed when using it like this.

Wired Charging

I tested the same set of phones with a cable plugged in, and the results were all pretty similar. That’s no great surprise, since they all support at least 30W USB C charging, which is the most the power bank can put out.

Using the S24+ as an example, it took 26 minutes to add 50%, hitting 29.7W at its peak and getting up to 38 degrees C. The other two phones had very similar results, within two minutes either way.

More for my own amusement than anything else, I also tried to charge my laptop from the S4. While there are a few small laptops that don’t need more than about 30W to charge properly, most need quite a bit more, and it showed.

The charge level didn’t go down while the power bank was plugged into my Lenovo Thinkpad X1, but it didn’t go up either. Putting out a consistent 24W, the S4 unsurprisingly drained quite quickly, but it never got particularly warm. I didn’t see a temperature above 40C.

It’s not really the intended use, but if you’ve got something like a MacBook Neo or a Microsoft Surface Pro, you’ll be able to get a useful amount of charge into it before the S4 goes flat. Anything else, well, you should be able to at least eke out another hour of work if you really have to.

Just like its output, the power bank is rated to charge itself at up to 30W. That was very much the case in my testing: it sat rock-solid at 29.1W for most of the time, before slowly dropping as it got closer to full capacity.

Charging the S4 from empty to 80% took 1 hour and 24 minutes, with the internal temperature never getting above 40 degrees. That’s pretty good, both the heat and the length of time. Topping up the final 20% took another half-hour, for a total charge time of under two hours from dead flat.

Verdict

I really like this power bank, and I’m not the only one. Everyone I’ve showed it to has commented on how good it looks and feels, and its feature set puts it a long way ahead of the competition.

The only problem is that its price is also well ahead of its competitors, and not in a good way. As I write this, you’ll pay around $78 for the KUXIU S4, which is inarguably quite a lot of money for a 10,000mAh power bank.

It’s genuinely great to have a slim, attractive, fast-charging wireless power bank that you can prop up on its stand to watch shows, attach to the back of your phone as you walk around, and rely on to not catch fire if it gets damaged.

Paying two or three times more than you would for a generic model with the same capacity, however, is a tough sell for many people. I’m not saying it’s not worth the money: as long as you value all the extras you get with the S4, I actually think it is. It’s just a shame you have to think about that at all.

I’m sure the cost will come down over time, and KUXIU does run sales now and again with reasonable discounts. For now, you can at least use the coupon code kuxiuglobal to knock 10% off the price, which helps reduce the sting a bit.

So, final word. The S4 is a premium product that’s genuinely better than it’s competition. As with so many other things in life, though, that quality is something you’re going to need to pay for.

All images via author