[General Accessories] vectron:
This is a review of Anker Astro Slim2 4500 mAh dual output External battery (5V 1A Input, 5V 1A dual output with built in hideaway cable for one of the output ports): http://www.ianker.com/product/79ANS4552-BA

Every time I start to think about extended battery, I run into a big question of what am I going to do with all my cases that no longer going to fit the phone. That is why I decided to explore external battery solution. I don't trust no-name ebay brands because those have overly exaggerated capacity rating. So I turned to a trusted brand, Anker, since so many people in this forum had a lot of positive things to say about their products. In comparison to our stock 3100 mAh battery, this Slim2 external battery is not over the top with its 4500 mAh labeled capacity. If you take into consideration all the conversion factors between external lithium battery, USB port transport, and back to phone's battery, we are talking about final capacity which could realistically be closer to 3100 mAh (and actually stated in the manual as 30% internal power consumption due to losses). What makes the battery stand out is it's unbelievable slim form factor and all the design details that go with it.

When you first take it in your hand you can't believe how light and slim it is. We are talking about 10mm slim! I actually took exact measurement with my digital caliper and found it to be 4.97" x 2.52" x 0.41" (126.34mm x 64.08mm x 10.64mm) and weight to be 4.1 oz (116g) which also includes built-in micro-usb cable. I can see that a lot of thought went into it's design. The case of this external battery is made out of tough plastic with a matte finish and sides have a rubbery finish for a nice grip. The form factor is very slick, something that can go easily into your pocket or purse or even carried in one hand attached externally to your phone. The unit has one micro-usb input port which is cleverly covered by hideaway micro-usb output cable/connector, and another regular usb output port. Pretty much it eliminates a need to carry any external cables since the one you need for your Android device is already built-in. The cable for that external micro-usb connector is flat, flexible, and just long enough to wrap around the end of the battery pack, and it should be sufficient to connect to any phone or tablet. As part of the accessories that come with Slim2, you also get usb-to-micro-usb extension cable with additional mini-usb adapter and Apple 30pin adapter. This second regular usb Output port also comes very handy for another important reason. If you look at the pictures I took, you can see that hideaway micro-usb connector has trapezoid shape. It should work fine with most of the slim or rugged cases that have silicone or tpu inner shell/bumper surrounding micro-usb port opening. With my UAG case is was a very close call where I had to push it in with some force. This hideaway port will not work with Defender case due to its inner plastic shell suited and standard rectangular port opening. That's where 2nd usb output port comes in handy to use external usb cable with a regular micro-usb connector.

There is no power button, instead you have auto on/off capability and display of battery capacity using 4 led lights partitioned in 25% increments. Every time you plug/unplug power cable those lights lit up to show you capacity level or charging level. Also, auto shut off reassures that you will not overcharge the battery once it reaches 100%. I charged this battery to 100% (indicated by 4 solid lights), and used with my Note 2 which was down to 55%. To my surprise charging time was very fast considering it has 1A output, and I was able to get my phone back to 100% within 1.5 hour with 2 led lights remaining thus indicating that battery still had 50% of charge left. That is consistent with my assumption of battery capacity to be around 3100 mAh.

Overall, I'm very pleased with Slim2 as an emergency battery pack. It's slim, easy to grip, light weight, small footprint, NO need for external cables (unless if you have a case like Defender), and ability to charge 2 devices simultaneously. Furthermore, if you remember my mod with clip stand from a car mount, I actually found it to fit together really well which is great, for example, while watching a movie and charging your phone up at the same. Everything is captured in pictures below!

With a clip-stand: