Bests & Worsts Reviews from Amazon

I grabbed this Jackery Mini 3200mAh Power Bank) during an Amazon Lightning Sale. Previously I have tested the Jackery Bar 5600mAh Portable Power Bank and liked it very much. This new unit did not disappoint. [Mechanical Design] The body of this Jackery Mini unit is compact and sturdy. It has a highly-polished aluminum case with no rough edges. There is an on/off button and a 4-LED battery status indicator. Unlike its bigger brother, this unit has no LED flashlight function. [Electrical Design] The unit seems to be designed to conserve power as much as possible: - It does not auto-start when an USB device is plugged in. You need to press the power button to get it started. This reduces the standby power to extend the battery's shelf life. - The unit will power off automatically if no load is detected within 30 seconds. So you don't have to worry that the unit got accidentally turned on and drains its battery. - The blue status indicator lights up when the power button is pressed, then goes off in 10 sec even though the USB port is still powered. Again, this is done to reduce power consumption. The down side is that you can't tell the battery status during charging, unless you press the power button again. [Battery Capacity] I used the DROK Dual-USB Output Charging Detector to measure the output voltage and current of this unit, with a 5-ohm power resistor as load. The unit sustained a regulated output of 0.94A at 4.8V (4.5W power) for 127 minutes. The total output energy is 4.5W*127/60 = 9.5Wh. Assuming the energy conversion efficiency is 80%, the energy stored by internal battery is 11.9Wh. The battery capacity is therefore 11.9Wh/3.7V = 3.2Ah, exactly as advertised. [Status Indicator] There are 4 LED dots in the status indicator. Naturally people may expect each dot to represent 25% of the charge. This is quite close to the actual behavior I observed: 4 LED = 80-100% 3 LED = 55-79% 2 LED = 25-54% 1 LED = 10-24% blinking = 0-9% [Output Current] The output is rated as '5V 1A'. In actual testing with different loads, the most I can pull from the USB port is 1.16A, before its voltage starts to falter. So the current rating is accurate. [Charge Time] When being charged, the unit draws 0.98A initially. This current drops when the internal battery is nearly full. Total charge time from empty is about 3.5 hours. [Conclusion] The Jackery Mini is a very well-designed product, and it performs exactly as advertised. Its capacity of '3200mAh' may not look very impressive, but that's more than enough energy to charge up the 2100mAh battery in my phone (Samsung Galaxy S3) once, and that's all I needed it for. [Update on Nov 25, 2014] I took the Jackery Mini with me on a flight to the Far East. It proves to be a life-saver in keeping my cellphone alive throughout a 30-hour journey. I'm very happy with my purchase. [Update on Oct 27, 2015] - Added photo to show size comparison between various power banks in the 2600-3200mAh range