Bests & Worsts Reviews from Amazon

The price of this KMASHI 10000mAh MP816 Dual USB Power Bank is lower than most other power banks with half of its capacity. Previously I have good experiences with several KMASHI products (such as the KMAX-812 4400mAh Rechargeable Backup Battery Pack). That's why I decided to give this unit a try. [Battery Capacity] Most lesser-known battery packs tend to exaggerate their capacity ratings. So I conducted my own test to verify the claim of '10,000mAh'. I connected a 3.3 ohm power resistor to the 'OUT2' port (which is rated up to 2.1A max). The unit is able to supply 1.5A at 5V for 241 minutes, before shutdown. This means a total output energy of 30Wh (5V * 1.5A * 4hr). Assuming conversion efficiency of 80%, I can then estimate the internal battery to be about 10,000mAh (3.7V * 10Ah * 0.80 = ~30Wh). So the advertised capacity rating is accurate. [Output Current] During my testing, I discovered that OUT2 port is unable to sustain any load current greater than 1.8A, even though it is rated as '2.1A max'. The OUT1 port, on the other hand, is able to supply 1.1A, or slight higher than the rated '1.0A max'. This is disappointing since my main goal is to recharge my Barnes & Noble NOOK HD+ Tablet during long trips. The Nook has problems with most power banks I tested. It will try to draw 2A charging current initially. But if it can't, it will drop the current to 0.45A instead. In this case, the Nook can draw 1.1A from OUT1, but only 0.45A from OUT2. [Status Light] The MP816 has a 4-LED battery status indicator light. According to the instruction sheet, each LED is supposed to represent 25% of charge. My actual testing showed that the status light is highly non-linear: 4 LED = 61 to 100% 3 LED = 32 to 60% 2 LED = 19 to 31% 1 LED = 4 to 18% blinking = under 3% This is a common problem with most power bank units: you can't reliably tell the remaining battery capacity based on status lights. One exception I found is the PNY Dual-Port 2.4 Amp 7800mAh PowerPack. It has a digital status indicator that can report the battery status accurately - down to 1% according to my test. Sadly, the PNY unit is also unable to supply 2A for my Nook. [Power Button] One quirky thing I noticed about the power button: it needs a very short press to turn on. If I press and hold it for 1 sec, the power remains off. This behavior is opposite to that of most other power banks. [Recharge Time] During recharge, the MP816 draws up to 1.5A - as long as your USB power source can supply it. So it takes about 8 hours to fully recharge the internal 10Ah battery pack. But if your USB power source can only supply 0.5A, then it could take 20 hours! One drawback I discovered is that there is no pass-thru charging. That means while you are charging the internal battery of the MP816, you are unable to recharge anything else from OUT1 or OUT2 ports. [Bottom Line] Given its low cost and high capacity, I still consider this KMASHI unit a very good value. I just have to remember that the '1A' port actually charges my Nook faster than the '2.1A' port. [Footnote] I used the PortaPow USB Power Monitor to measure the unit's input and output currents. It is indispensible in testing charging rate of my USB devices. See my review on it for details: http://www.amazon.com/review/RVRNRAC9JJYOP [Update on Mar 18, 2015] I have tested the Yoobao SP2 10000mAh Dual USB Port Power Bank and found it capable of charging my Nook HD+ at 2A. See my review on it for details: http://www.amazon.com/review/R2NOFH93OIVY5C/ [Update on Jan 18, 2016] In case you're looking for a high-capacity power bank that supports pass-thru charging, I recommend the MoKo 9000mAh Dual-Port Portable External Battery Charger. It is much better than the Kmashi MP816 because: - It is more compact - Comes with an LED flashlight - Able to charge my Nook HD+ at 2A from any port - It puts out nearly the same total energy (29.5Wh) as the MP816, despite lower advertised battery capacity (9000mAh vs. 10,000mAh)