Power banks, these small gadget that can save you in critical situation when your smartphone dies for power and no power resource near by. I was in a middle of long meeting when my iPhone showed the Red indicator of remaining power to found out that I forgot my charging cable and I have to drive home depending on Google maps as meeting was in Long beach, California and I live in the Valley 55 miles away. I was saved by a co-worker whom I found using a Power bank to charge this cell, I've asked him to borrow his Power bank when done and luckily he handed it to me saying he is done and he is not sure if his power back still have power, I thanked him and plugged in my iPhone into the power bank and I was lucky that it charged my cell half way before power bank died. Since then I decided to get one of these life saver gadgets and here what I found best power bank.
First the price range is from $15 to $40 and here is the winner list.
Anker PowerCore 20100
This powerful power bank Anker PowerCore has Simultaneously dual 2.4A/5V output through both USB port so it can charge two sets at the same time so you can charge a Samsung S6 and iPhone 6 at the same time to full charge and about 2 hours and the devise will still have more juice for more devices.​
Anker Astro E1 5200mAh Candy bar-Sized
Anker Astro is smaller and cheaper model features PowerIQ charging technology. That means that you can plug it in any type of device and this smart port will set the charging current to match the maximum charging rate that your device can safely handle. The port is rated at 5 VDC and up to 2 Amps. It has 4 LED light to indicate the level of the charge it holds so 4 dots represent 100% charged capacity, 2 dots is 50% charged capacity and so on.
Lumina 15000 mAh Ultra Compact.
The Lumina 1500 features ​high powered 15,000 mAH capacity with two USB outputs, 5V 2.4A with a total max output of 5V 4.8A. LED power display allows you to accurately keep track of remaining power in your Power Bank. Durable aluminum alloy outer casing sports a premium look while offering extremely durable protection.
RAVPower Portable Charger 22000mAh
The RAVPower is a very powerful one for 3 Charging Devices with 3 USB ports for a total current output of 5.8A​ which means it can hold a good amount of chargers for all your devices and it comes supplied with 2 USB-A to micro-USB cables. The new and improved iSmart 2.0 adjusts current and voltage to minimize charging time, Meanwhile the Panasonic Smart IC frequency technology provides a safer and higher current conversion of this portable charger.