So I've been trying to figure out how to charge my Transformer Prime from an external battery charger when I'm not near AC, but was having a terrible time making it work. But I solved it.
First - realize your Transformer Prime requires a minimum of 12 volts to charge, and MOST of the external chargers are 5v only. I purchased the Anker Astro3 10000 mAh charger. It has both 5v AND 9v/12v outputs. Other chargers might work too, but make sure one of the outputs is a minimum of 12v/2A.
Second - there is NO connector in the box that fits the proprietary power/data connector for the Transformer Prime. But with the purchase of a Female-to-Female USB connector (I bought mine at Fry's, but Amazon also has them) you can make it work.
Connecting it up - It uses a few of the connectors that come in the box... To make it work: a) you plug the included 12v cable into the Astro 3, then b) you plug in one of the included power size adapters into the 12 volt cable (you'll figure out which one), then c) you plug in the included power-to-USB cable into the power size adapter, then d) you plug in the female-to-female USB connector that you purchased, then e) you plug in your original USB-to-Transformer Prime cable.
Then voila - done! It sounds complicated, but it's not really, and once you set it up you don't need to take it apart again.
The second benefit of this charger is that you can simultaneously charge your phone, in my case an HTC LTEvo, but it can be essentially any phone including an iPhone. My Transformer Prime and my phone are both charging nicely as we speak....
First - realize your Transformer Prime requires a minimum of 12 volts to charge, and MOST of the external chargers are 5v only. I purchased the Anker Astro3 10000 mAh charger. It has both 5v AND 9v/12v outputs. Other chargers might work too, but make sure one of the outputs is a minimum of 12v/2A.
Second - there is NO connector in the box that fits the proprietary power/data connector for the Transformer Prime. But with the purchase of a Female-to-Female USB connector (I bought mine at Fry's, but Amazon also has them) you can make it work.
Connecting it up - It uses a few of the connectors that come in the box... To make it work: a) you plug the included 12v cable into the Astro 3, then b) you plug in one of the included power size adapters into the 12 volt cable (you'll figure out which one), then c) you plug in the included power-to-USB cable into the power size adapter, then d) you plug in the female-to-female USB connector that you purchased, then e) you plug in your original USB-to-Transformer Prime cable.
Then voila - done! It sounds complicated, but it's not really, and once you set it up you don't need to take it apart again.
The second benefit of this charger is that you can simultaneously charge your phone, in my case an HTC LTEvo, but it can be essentially any phone including an iPhone. My Transformer Prime and my phone are both charging nicely as we speak....
I also always have mine in it's rugged little minisuit & docked, so the battery charge I usually get from an overnight plug-in is really enough to get me through the day, though I do use it heavily. If you were without power & needed a really long charge avail., camping, power outage, don't use the keyboard, etc., you were addressing how a person could fill those needs, sorry.
