Bests & Worsts Reviews from Amazon

I already own two 10,000mAh dual port power banks, the KMASHI MP816 and the Yoobao SP2. However, although they both offer two ports rated '2.1A' and '1A' respectively, they are unable to sustain a total output current of 3.1A at the same time. That's why when I saw this AmazonBasics 10,000mAh Portable External Battery Charger (PB10) advertises a total output current of '3.4A', I just have to check it out. [Physical Size] The AmazonBasics PB10 is about the same size as my phone (Samsung Galaxy S3), just slightly thicker. The case is completely made of plastic, but it feels sturdy and does not look cheap. It is significantly thinner and lighter than my two other 10,000mAh power banks. According to my electronic scale: - AmazonBasics PB10: 222g - Yoobao SP2: 265g - KMASHI MP816: 280g [Output Current] There are two USB ports. The user instruction says the port marked with one lightning symbol is rated '1A', while the one with two lightning symbols is rated '2.4A'. However when I tested charging my Barnes & Noble NOOK HD+, the '1A' port is able to charge at 1.9A, while the '2.4A' port is only able to charge at 0.46A. I assume the 2.4A port is designed to work with Apple products only. While charging the Nook from port1, I connected a 2.5-ohm power resistor as load to port2. The PB10 is able to produce 1.94A from port1 plus 1.89A from port2, for a total current of 3.83A! This is even higher than the advertised 3.4A total. I left the power bank running at maximum load for about 30 minutes without any problems. The top part of the unit became warm to the touch, which is to be expected. [Battery Capacity] I tested the capacity of PB10, by connecting a 2.5-ohm resistor to port2. The unit produced a regulated 4.95V at 1.85A (power=9.15W) for 229 min. The total output energy is therefore 9.15W * (229/60) hr = 34.96Wh. This is more energy compared to my two other '10000mAh' power banks, tested under similar test conditions: - The KMASHI MP816 produced 30.0Wh, or 15% less - The Yoobao SP2 produced 30.9Wh, or 12% less If we assume the power conversion efficiency is 90%, then the internal battery capacity can be estimated as 10500mAh, slightly higher than advertised. [Recharge Time] While recharging from a 2A USB AC adapter, the input current is around 1.7A initially (it drops when the battery is nearly full). Total recharge time from empty to full is just 6-7 hours. However, if you try to recharge the PB10 from a 500mA USB port, then it will take one whole day. One minor problem I found is that: the PB10 does not support pass-thru charging. That means when its internal battery is being recharged, it turns off both its USB ports. This is inconvenient because I cannot connect my phone and this power bank in series, then recharge both from the same USB AC adapter. I should mention that both the Yoobao and KMASHI 10000mAh units are unable to support pass-thru charging. But lower capacity units such as Jackery Bar 5600mAh and KMAX-812 4400mAh are able to. It could be by design, to limit the input charging current. [Bottom Line] The AmazonBasics 10,000mAh power bank is a well-designed product, both electrically and mechanically. According to my testing, both its battery capacity and maximum output current are even better than advertised. Now that's the sign of solid engineering design! [Update on Aug 31, 2015] In case you are looking for a high-capacity power bank that supports pass-thru charging, consider the MoKo 9000mAh Portable External Battery Charger. It delivers 29.5Wh of total output energy (vs. 35Wh for the PB10) at up to 3.2A. It is more compact, but not as slim as the PB10. [Update on Mar 13, 2016] Uploaded a picture showing some of my favorite power banks of various capacities: AmazonBasics 10,000mAh, MoKo 9000mAh, KMAX-812 4400mAh, and TYLT 3200mAh.