I carry two types. One is a regular plug in travel charger by Motorola for my z3 in the room, and the other is a Fuel Rod for walking around the parks.
We picked up an Anker 20K mah portable charger a couple of years ago, it can charge both of our iPhones twice over and charges up overnight. I made sure we had some shorter firewires just to keep the wire mess to a minimum, but it worked great.
I've got an Anker PowerCore 10000 Portable Charger. Only $21.99 at Amazon right now. It charges overnight (maybe even faster than that) and it works for both my Android phone and my sister's iPhone. Not that heavy and works great.
I picked up a charger from Marshalls for under $10 before our last trip and clipped it to our draw string backpack with the carabiner clip or to my belt loop when we went bagless. It kept both of out Iphones charged and we recharged it overnight.
Another vote for Anker here! I love it (My nieces who forgot to bring a power block also love it since I could charge multiple phones with one full power block!)
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