What do I need to know to buy a portable charger for my iPhone 5S? Thanks!

I'm going on vacation so I want to have a portable battery bank. I've found several choices for a portable charger for my iPhone 5S. The Voltage by Urban Beatz with 2200 mAh , iHome with 2200 mAh, and Samsonite with 4400 mAh. Would any of these be too powerful? Thanks!