Unfortunately it's a smoke alarm battery. 
I've also tried running it off of 5 AAs that the robot kit came with. They both behave the same.
Dave said I didn't connect the grounds. I'm just using one power source, isn't it all one ground?
I'm definitely a beginner with electronics. Let's say it's grossly underpowered. Would that cause the PING sensor to blink at an erratic fast pace? It also seems odd to me that when just on USB-power only, the PING behaves correctly even though the motors are barely turning.
Do I need to have a separate power supply for the motors? Do I just need more amps?
Any other helpful hints are welcome.