SparkFun 5V/1A LiPo Charger/Booster Hookup Guide
Contributors:
MTaylor
MTaylor 
Connecting a Load
Eager to get your 5V? Just connect up to the output terminals!
Closeup of the output terminals are marked with polarity.
But there's always more to know. An ideal booster circuit translates all input power to output power, so if the output is providing 5V @ 1A, or 5W, 5W must also be going into the booster. But if the input voltage is down to the battery lower limit of 3V, it will require 1.666A! With an efficiency of around 85%, it requires almost 2A on the input!
Here's a graph of the charger booster's measured performance:
Input current (right scale) and output voltage (left scale), shown as a function of output load. Notice that the output voltage sags slightly, but is pretty well regulated, and that input current is always larger than output current for a booster circuit.
Input and output power is shown (left scale), as well as overall efficiency (right scale).