External Charger/Power Pack

[just jake]

I thought I would turn to the experts if you will. I have had my Droid A855 since February and love it. Like most of us there are some down sides or problems we tend to live with by owning this phone. My biggest complaint, and have seen it mentioned by others, is the battery life. So after looking around and reading other reviews I thought I would ask here.
I am thinking of getting an EXTERNAL SOLAR CHARGING/BATTERY pack to keep with me when I am going to be out for any length of time and not in my car. I have seen a few of these items offered on the net from eBay to Amazon but not sure which one to buy and what should be the proper output voltage so I don’t damage the Droid battery. Also the price on these items range from under $10 to over $50.
Have any members used any device of this nature? If so which item do you recommend? What is the proper output voltage?
Many thanks for your time and consideration on this request.