The other day I was riding to work and noticed at the first stop light that my volt meter dropped from about 13 to about 5 while the bike was idling. When i opened the throttle to go, the voltage went back up. Bad battery?

 

Don't guess! If you don't have a service manual, go to the DIY Electrical section where you will find Stickies on checking your charging system. They will help you identify the culprit.

 

More likely a loose connection. Most modern Harleys won't run on 5V.
Start by checking the connections to the voltmeter.

 

Did you get a check engine light or battery light? I had to replace voltage regulator on mine. Take the primary cover and smell. If it smells like burnt electronics then its your stator. Make sure your battery reads 12.4 or better while not running.