I have posted earlier about how to manage your power-hungry smartphone. Lifehacker just endorsed the top 5 external juicers as nominated by their readers. I think that these are good chargers at a decent price but I don’t prefer to use the larger of these batteries. For business you want to minimize carrying around heavy things and these batteries are so large they are not business-friendly when sitting in your pocket.
I balance charging power with minimizing weight and size. To this end I prefer the smaller, 3200mAh, Anker batteries. The price is close to $20 so you also get a good value. It will fully recharge almost any smartphone from near dead effectively doubling the life of your phone. It also charges through your phone’s USB charging cable.
If you have a heavy charging load and room to carry something heavier than pick up some from the Lifehacker list. Otherwise go slim and light and cheap.