TechnologyTell Review: Justin 2000mAh Slim Power Bank

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While cruising through the product-packed halls of CES 2015, I couldn’t help but notice groups of people leaning up against sections of wall all along the outskirts. Although some were merely looking for a place to sit and eat food, the rest of them were tethered to outlets.

I saw tablets, smartphones, and laptops sucking away in order to sustain their users for a few hours longer. In some cases, these people weren’t more than 10 meters away from some booth showcasing, among other things, external battery packs.

While many portable power devices can be considered somewhat cumbersome, there are some no larger than a short stack of credit cards.


Had any of the before-mentioned people at CES 2015 owned the Justin 2000mAh Slim Power Bank, they would have been able to give their mobile devices a boost of energy on the go. This slim power bank is as thin as three quarters and just a bit longer and wider than your standard credit card. If, for whatever reason, you couldn’t fit this in your wallet, it’s certainly pocket-friendly.

Justin 2000mAh slim power bank box

Comes with a great cable and adapter tips

This slim power bank features a sleek look with its brushed aluminum body. A thin line of blue plastic peeks out from being sandwiched in the middle.

The “business end” of this battery pack hosts a single Micro USB port and a power button. This battery has auto-detect for when you plug in another device. You can’t really get any more basic or lightweight than this.

Like most external batteries out there, this one uses a four-LED power indicator gauge. Each dot represents a 25 percent charge threshold, as indicated by the numbers scribed alongside the lights. Just keep in mind that what you see is merely a rough estimate. When measuring the mWh going in to the slim battery pack, with a PLX Devices Legion Meter, the three lit LEDs versus the actual charge level were a far cry from each other.

Justin 2000mAh slim power bank top

Sleek, thin form

The convenience of battery capacity in such a compact form comes at a price. The output of this slim power bank is only 5V/1A and the input maxes out at 5V/800mA. These are the listed values (the effective input rate fluctuates between 470mA and 680mAh, from testing). If your smartphone or mobile accessory charges normally at 5V/1A, then you’re set! Otherwise, newer devices that can charge at a faster rate (e.g. 5V/1.5+A) will feel power only creeping in.

Included with the Justin slim power bank is a short Micro USB to Micro USB cable that comes with a pair of adapters: female Micro USB to male USB, and female Micro USB to female USB. The former will be more commonly used, as it lets this battery charge up from USB ports or wall adapters. You also get a faux leather wallet with adhesive mounts for the slim power bank on the inside. Opposite is a tidy pocket that comfortably holds a credit card and ID.

Battery Performance

My favorite part of the Justin 2000mAh slim power bank (aside from the form, of course) is how the LEDs remain lit while charging out. I also appreciate that the LEDs blink while the battery is charging up, as is common with most. But the reason I like lit LEDs when the battery is charging out is because one glance lets me know if it’s done or not.

Justin 2000mAh slim power bank case

The carrying case is a thoughtful touch

When a battery pack remains dark while charging out, I have to manually check the devices. Sure, some may call me lazy, but I prefer to have that visual indicator, especially if a gadget is off and charging. And once the slim power bank is full, all four LEDs glow solid blue.

Since there is only the single Micro USB port, there is no passthrough charging. Thankfully this slim power bank is of a low enough capacity where charging it back up doesn’t take longer than it has to. It is a little bit odd that the input charge rate is 5V/800mA instead of the basic 5V/1A. But I guess it’s these low(er) charge rates that keep the battery cool to the touch while working.

Note: Most external battery packs I’ve ever purchased and used came only partially charged, so I’ve always made it a habit to fully charge them before use. I tend to fully charge and discharge a new battery a few times, just so I can level out the charge states of the individual cells. It helps to maximize the battery’s manufacturer-listed potential.

Justin 2000mAh slim power bank thickness

Just like that – three quarters

The standard efficiency rating of external battery packs currently on the market is 70 percent. This means that 30 percent of the battery’s listed capacity is consumed while charging up devices. So, for example, a standard 1000mAh battery would effectively deliver 700mAh of energy.

Right out of the box, the Justin 2000mAh slim power bank was able to deliver a total of 41 percent charge, or 1255mAh of usable energy, to my Samsung Galaxy Note 4 battery (3220mAh). That’s equivalent to 62.8 percent efficiency. A bit below average. However, additional charge cycles brought up the values to a peak of 74.0 percent and an average value of 69.9 percent. That average is equivalent to 1398mAh of usable energy. It meets the average, sure, but I’ve noticed this to be normal with smaller/slimmer battery packs

So what can you do with 1398mAh of battery energy? That’s good for 0.43 full charges to a Samsung Galaxy Note 4 (3220mAh), or 0.77 full charges to an Apple iPhone 6 (1810mAh), or 0.31 full charges to a 7″ Kindle Fire HDX (4500mAh).


For the average user, who wants the convenience of extra energy without adding much to personal carry, the Justin 2000mAh slim power bank fits the bill. It’s thin, light, and delivers more than enough to power gadgets in those crucial times of need. Most smartphones should be able to last half a day longer of heavy use.

The only criticism about this slim power bank is the very average efficiency rating. And that’s not even a negative observation either. It charges in/out, doing its job well without anything fancy or unnecessary. I like the short, flat-ribbon Micro USB cable, and the added holder is a nice touch. If you’re a fan of brushed metal and want a simple battery pack, this Justin 2000mAh slim power bank will suit you well.

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