After Four Hours of constant Radio playing, and no interrupting phone calls or SMS messages, our Battery Bank had given out.
My device was toasty hot, as the processor was in overdrive. I clocked in nearly a gigabyte of Data usage, and this entire time was

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using constant 3G radio listening, something that sucks battery life like no tommorow! This can be easily doubled in time of heavy usage (Wtihout constantly listening to the 3G radio)
Taking into account that this is 2 batteries in one, I'd assume that's 2 hours each, and (including my device's OEM battery) a grand total of 6 hours of overdrive usage, something that can last me through a flight delay at an airport without Charging ports! I'd say this is pretty close to a significant advantage, since my TP with only the OEM battery will last me 1 and a half hours of such heavy 3G usage
So, what's the conclusion?
I'm VERY satisfied with my investment. OEM batteries can cost up to $30 each, and will not last for future device purchases. Our friendly, 5V DC 1000 mAh battery will last us for years. It can charge any USB device (So far, I tested my Bluetooth device, Zune, and even an external HDD that uses two USB ports!) and its size and weight are made up in this great, universal advantage.
I've even had instances of coming home (with light usage) with only 2 bars gone (Meaning I had a good 3 hours left of heavy usage, after a 10 hour day). Aside from size, the only other disadvantage is it doesn't allow charge/discharge simultaneously. So you need to use your device without a battery bank mid charge.
The only thing left to do is get a solar panel for it.