Bests & Worsts Reviews from Amazon

[Update on Oct 31, 2014] My review was written and posted for the 5200mAh version. Unfortunately, Amazon loves to shuffle products around. So now my review appears under the 16000mAh product page and who knows where else. I don't like it either, as it creates a lot of confusions among readers. == Original review for 5200mAh version follows === I need a portable charger for my Samsung Galaxy S3 and various Android tablets. Previously I have had good results with two other Poweradd products I purchased, so I decided to try this Poweradd LE011 5200mAh Power Bank with LED Flashlight. There are many cheaply-built power bank units with poor output regulation and inflated battery capacity ratings. That's why I conducted a test to measure the true capacity of this Poweradd unit. First, I made sure that the internal battery pack was fully discharged and recharged for several cycles. Next, I connected a 5-ohm power resistor as load to the USB port, and measured its output voltage and current over time. Here is what I have observed: - For the first one hour, the unit generated a very well-regulated 5.02V at 0.96A, or 4.8W of output power - After 70 minutes, however, the output voltage (hence power) starts to drop linearly with time. It dropped from 5V down to 4.75V over the next 100 minutes - Right after 172 minutes, the power cut off completely. (see the chart I uploaded to 'Customer Image' section for details) Based on the above data, I can estimate the internal battery capacity through energy calculation: - Average output power = 4.7W - Runtime = 172 minutes - Total output energy = 4.7*172/60=13.47Wh - Assuming conversion efficiency of 80%, input energy required = 18.84Wh - At 3.7V, the internal battery's capacity = 18.84/3.7 = 4.55Ah Therefore my measured battery capacity is 4550mAh, or 88% of the advertised capacity. To put this capacity number in perspective: it is enough to recharge the 2100mAh battery in my Samsung Galaxy S3 for 1.5 times (since part of the energy is lost during conversions). By the way, my other two Poweradd products also show slight discrepancy between their measured and rated capacities: - The Poweradd 2600mAh Ultra Slim Power Bank with Mini USB flashlight has a measured capacity of 2490mAh, or 96% of rated value. - The Poweradd 5000mAh Dual-Port External Backup Battery Pack has a measured capacity of 4380mAh, or 88% of rated value. The battery status indicator is very good. It uses 4 LED 'dots' to give a fairly accurate indication on the remaining battery capacity. Based on my observation: - 4 dots = 77-100% (approximately) - 3 dots = 57-76% - 2 dots = 39-56% - 1 dot = 21-38% - 1 blinking dot = below 20% The LED flashlight, on the other hand, is very disappointing. The light is so dim that it is weaker than any of my keychain LED flashlights. In fact, the blue status indicator from the other 5000mAh Poweradd unit is about equally bright. Overall, I consider this Poweradd unit a good value (4-star). I would give it a 5 if the LED flashlight were a little more powerful. [Update on Oct 28, 2013] I tested the PowerBot PB5600 5600mAh Power Bank which is currently available at the same price. The PowerBot unit offers 10% higher capacity and a more usefull LED flashlight. The Poweradd unit still has the advantage of being more compact. [Update on July 25, 2014] If you are looking for a battery pack with a real powerful flashlight, I highly recommend the KMAX-812 4400mAh Rechargeable Backup Battery Pack. It is rated 4400mAh, but actually can deliver more energy than this PowerAdd '5200mAh' unit. See my review on it for details. http://www.amazon.com/review/R2FI5S951Q1ILT/