tl;dr: Slightly pricey, but it'll be worth it when you need it!
I've carried a small external USB battery pack with me for the past few years, ever since I started relying on my iPhone as my only camera, phone, reading device, and emergency-backup-Internet device. And there have been many times where I would've been up a creek (or more literally, lost in the middle of an unfamiliar city!) without it.
But the little battery pack I tote around is only really for emergencies—it can barely top off my iPhone when the phone is already at 50% capacity, and if the iPhone gets below 10%, it'll struggle to even maintain the current charge if I have to use the iPhone while charging!
Enter the modern 10000+ mAh external battery pack. For review purposes, I was given a Intocircuit® Power Castle 15000mAh 4.8A Dual USB External Battery Portable Charger with Built-in Flashlight (say that three times, fast!). This battery pack provides two USB ports, both of which are capable of charging any modern device at a decent clip with up to 2.4A of power draw per port. My iPhone and iPad both got two full charges before the unit itself needed a recharge, and when using it only with one iPhone 6, I could get between three to five full charges, depending on how much I used the iPhone on a given day.
If used conservatively, you could keep a phone going full-tilt for an entire week without any external power access at all!
Some of the nice features of this charger:
- The LCD on the front gives all the information you need at a glance—mainly the big "X%" charge indicator, that goes up while you charge the unit, and down while you pull charge from the unit. It's easy to see how much charge remains, and the screen is responsive when you plug in a device to charge it or press the 'ON/OFF' button to quickly check remaining capacity.
- It's gimmicky, but the LED flashlight did come in handy once or twice. Just double-click the 'ON/OFF' button to activate. It's not too bright, but it's good enough for finding your way in the dark if need be.
- The hardware fits together pretty well, and all cables, plugs, ports, etc. feel solid enough to last a few years. It's not Apple-quality, but the thing doesn't cost as much as something similar from Apple would cost, either!
Some things I didn't like (but for the price, I'm willing to accept without too much judgement):
- It takes a very long time to charge the unit itself; even if you have a 2A+ wall wart to charge the unit, it will take many, many hours to go from 0% to 100%. Typically not a huge deal, but when I'm on longer trips, I don't always have a full day I can let the unit sit and charge somewhere.
- The front of the device looks pretty nice, almost elegant, in fact, but is marred by the cheesy 'Intocircuit' logo. Not a major flaw, but sometimes it's the little things...
As another fun test, I even plugged in two Raspberry Pi model 2 computers to the Intocircuit, and under light load (they were both running webservers for utilitarian purposes), they ran for over a day with some charge left in the Power Castle!
Overall, this is one of the best and most capable battery packs I've used. The LED is mostly a gimmick, but the main purpose of the device—charging and recharging your mobile devices over and over without needing a wall plug—is achieved in spades. I would definitely recommend this to anyone who needs to go on long trips, especially when power is a precious commodity!
You can purchase the Intocircuit Power Castle Battery Pack from Amazon for $39.99.
About 8 months later, this battery pack is still going strong, and even after sitting in it's case for about 3 months, it has 86% of it's charge available, which charged up both mine and my wife's iPhone recently when we needed to run somewhere that didn't have reliable AC power. Still recommended if you need something like this!