This is the English edition of a review from my Japanese YouTube channel, iestaLife. I review gadgets from my home studio in Japan, so product links go to Amazon Japan.
Quick take
CIO sells its slim SMARTCOBY SLIM 5K MagSafe-style battery in two versions that look identical: a High Performance model that charges faster, and a Safety model that limits heat. In my test the High Performance model was faster, ran about 10°C hotter, and also delivered a little more charge. If you mostly charge in a bag, I would pick the High Performance model.
What I tested
- CIO SMARTCOBY SLIM 5K, High Performance model (5000 mAh, Qi2)
- CIO SMARTCOBY SLIM 5K, Safety model (5000 mAh, Qi2)
- iPhone 17 Pro Max with no case, starting at 18%
- Room temperature around 23°C, phone left untouched while charging
What I found
- High Performance: 18% to 42% in 30 minutes, 61% after about an hour, 76% when the battery ran out.
- Safety: 18% to 50% in one hour, 60% at 90 minutes, 72% when it ran out after about two hours.
- Peak temperature on the High Performance model was 43°C. The phone itself reached about 39°C. Warm, but not too hot to hold.
- The Safety model was at about 32.5°C after 12 to 13 minutes of charging. I only measured it once, so this is not its peak, but it felt clearly cooler.
- Both cost 5,980 yen at the time of recording, and both come in silver and black.
Side by side
| High Performance | Safety | |
|---|---|---|
| Photo |  |  |
| Price | 5,980 yen | 5,980 yen |
| 1 hour | 61% | 50% |
| Final | 76% | 72% |
| Temp | 43°C (peak) | 32.5°C (12 min) |
In an earlier video I also tested the Safety model against an unbranded battery sold in Japan as "8000 mAh". The CIO reached 72%, while the "8000 mAh" one only reached 69%. My rough takeaway: over wireless charging, about half of a battery’s rated capacity ends up in the phone. To fully charge an iPhone 17 Pro Max this way, you would want something closer to 10,000 mAh.
Who it’s for
- High Performance: you want the most charge in the least time, and the battery usually sits in a bag.
- Safety: you charge while using the phone, use it outdoors in summer, or simply want the cooler option.
- Neither: you need a full charge of a large iPhone from empty. 5000 mAh adds roughly half.
Watch the video
The video is in Japanese. The temperature checks on the High Performance model start at about 4:00, and the Safety model is measured from about 9:00.
Limitations
I ran each model once, at home, with a simple non-contact thermometer. The difference in final charge may not repeat every time. The two models look the same, so label them if you own both.
Products
CIO SMARTCOBY SLIM 5K (High Performance): on Amazon Japan
CIO SMARTCOBY SLIM 5K (Safety): on Amazon Japan
The Amazon Japan links above are affiliate links. As an Amazon Associate, I earn from qualifying purchases. Check the listing for the exact model, current price and shipping availability in your region.
More reviews in English
All Chargers & Cables (29) →Browse all English reviews →
This review is also available in Japanese.