Charging
ESR CryoBoost vs KUXIU K1 Ultra: desk charger or power bank?
Two ways to charge an iPhone, Apple Watch and AirPods. Which makes more sense at your desk, and which earns a place in your bag?
By WannabeShepherd · · Updated
Choose the job before the charger
For a permanent desk setup, I would choose the ESR CryoBoost: cooling made a meaningful difference to charging my iPhone 12 Pro. For charging away from a socket, the KUXIU K1 Ultra adds a battery and a useful Watch charger. It is more versatile on the move, but thicker than I want attached to a phone in my hand. The later iPhone 17 Pro run narrowed ESR’s fan-on wireless gap to nine minutes behind USB-C, but the KUXIU remains untested on that phone.
Based on my two original reviews, using an iPhone 12 Pro in a thin MagSafe-compatible case, Apple Watch Series 10 and AirPods Pro 2. This is not a new simultaneous test. Ambient conditions were not documented as identical, and the older iPhone cannot establish maximum charging speed on newer models. Both products were supplied for review. ESR was subsequently retested with iPhone 17 Pro in October; those results are linked below. KUXIU remains an iPhone 12 Pro test. Neither establishes iPhone 18 Pro speed.
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| Use | ESR CryoBoost | KUXIU K1 Ultra 10,000mAh |
|---|---|---|
| Main role | Powered 3-in-1 desk charging station | Portable battery, charging stand and Watch charger |
| iPhone 12 Pro result | 0-80%: 79 min with fan; 120 min without | Approximately 0-80%: 144 min |
| iPhone 17 Pro follow-up | 0–80%: USB-C 46 min; fan on 55 min; fan off 67 min | Not retested with iPhone 17 Pro |
| Desk impression | Quiet cooling at normal working distance | Stable hinge and kickstand; thick when closed |
| Watch detail | 80% in 38 min in my test | Press the button to start Watch charging |
| Main compromise | Looser Watch hinge; no magnets in the AirPods area | Flashing Watch-charge LED and awkward USB-C placement |
| Travel evidence | Folding design assessed; not travel-tested | Portable design assessed; not a slim phone-attached battery |
At a desk, cooling is the useful difference
The clearest result in my ESR review was the fan-on versus fan-off test. The same iPhone 12 Pro reached 80% in 79 minutes with cooling enabled and 120 minutes without it. The wired reference was 62 minutes. That is a useful observation about this phone and setup, not a promise for every iPhone.
The fan was quiet enough that it did not bother me at a normal desk distance. With cooling disabled, the phone felt noticeably warmer. I judged that by touch rather than a temperature probe, so I would not attach a precise temperature claim to it.
The iPhone 17 Pro follow-up changes the ESR picture
In my October iPhone 17 Pro follow-up, the same ESR stand took 46 minutes over USB-C, 55 minutes with the fan on and 67 minutes with it off to reach 80%. Wireless runs used my PITAKA case. These are separate daily-use charging runs, not a controlled lab ranking. The KUXIU has not been retested with this phone.
The fan-on wireless run was nine minutes behind the wired reference in this setup. After several months of daily use and travel, I have not noticed hinge deterioration or visible wear; the Apple Watch arm remains looser than the main hinge. Read the full follow-up with charts and current desk photos before using these results to choose a charger.
In a bag, the battery changes the decision
The KUXIU makes sense when the alternative is packing a phone power bank, an Apple Watch charger and a small stand separately. Its aluminum body, strong magnets and solid rotating hinge made a good impression. I see it as a portable charging station that can sit on a table, not something I would keep attached while walking around with my phone.
My 10,000mAh unit is thick. I would consider the smaller 5,000mAh version for my own travel priorities, but I have not tested it, and its size, capacity and performance should not be inferred from this review.
Do not turn the charging times into a universal ranking
The KUXIU took 144 minutes to reach roughly 80% with my iPhone 12 Pro. That was slow for a quick top-up, although I did not notice uncomfortable overheating. The ESR result was faster in the published tests, but these are separate review observations, not a controlled comparison of every condition.
For this older phone, I would still use a cable when speed is the priority. Neither review proves how fast these products charge a newer iPhone at their advertised peak output.
The small details matter after dark
The KUXIU Watch charger needs a button press even when the phone is already charging, and its status LED keeps flashing during Watch charging. That makes it less appealing to me on a bedside table. When used as a stand with USB-C connected, the cable exits at the top, which is not my favourite arrangement.
The ESR has its own compromises: the Watch hinge feels looser than the main hinge, and the AirPods area lacks magnetic positioning. I would pick it for the desk, while choosing the KUXIU only when having a battery and integrated Watch charging outweighs the bulk.
Sources and further reading
This guide uses the following manufacturer references and primary sources.
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The original reviews
ESR CryoBoost Foldable 3-in-1
A foldable 3-in-1 charger tested at the desk with an iPhone 12 Pro, Apple Watch and AirPods, including fan-on and fan-off charging results.
Read review
KUXIU K1 Ultra 10,000mAh
K1 Ultra 10,000mAh tested with iPhone 12 Pro, Apple Watch and AirPods; bulky, with slower wireless charging.
Read review