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Dimensions: 103.5 x 51.3 x 49.5 mm/4.07 x 2.02 x 1.95-inches
Weight: 378 g/13.33 oz.
Accessories: USB-C charging cable, high strength nylon holster
The NPB 4 has multiple fast charge output ports and provides a maximum output power of 18W, which is enough for things like smartphones and tablets but not enough for heavier loads such as laptops.
The power bank has enough power to charge an iPhone about half a dozen times, or AirPods a whopping 32 times, and yet the power bank is small enough to be allowed onto commercial aircraft.
On the side of the NPB 4 is a touch sensor power level display which shows three blue LEDs when the charge level is approximately 100%, two lights for 70% and one for 30%.
Oh, and if you wonder what those little clips on the side do, well, they had me puzzled too. Apparently they allow the power bank to be connected to Nitecore's HU60 LED headlamp.
If you don't have this headlamp, they're a handy fidget tool.
From a safety point of view, the NPB4 has everything you'd expect from a modern power bank, including overcurrent protection, over-discharge protection, and short circuit protection, and everything is encased in a fire retardant polycarbonate shell.
But it's the waterproofing that I really like here. Normally, power banks are waterproof if, and only if, you cover the ports with rubber seals. Not the case with the NPB 4. Notecore used a high strength O-ring on the charging port and an advanced glue pouring technology to protect the internal components from water.
And it works really well!
But can you use it underwater?
Well, Nitecore says you can. Here's a video showing it in action both being charged and powering three devices, all while submerged:
I've tested this and, yes, it works fine underwater. However, I'd be cautious for a couple of reasons.
First, while it should be safe to charge it underwater, I have come across poor quality or faulty chargers where the metal parts are referenced (fancy word for connected) to mains power. I wouldn't want to have my hand in that water if that was the case.
Secondly, water is going to get into the cables and ports, potentially causing small short circuits. In my experience, some USB devices can start to act funny when this happens, and there is the possibility for damage.
Even Nitecore's manual is quite cautious when it comes to water:
This is why I'm not recommending you use the power bank while submerged. If you do, the risk lies with you. I'd also keep it away from salt water and chemicals.
However, this is a power bank that I've happily left outside for extended periods to power a camera or GoPro, and let it get wet while in use. It's highly resistant to rain and condensation, and the risk of problems is far less than if the power bank were submerged.