What causes a new battery on a 2002 Ultra Classic to die?

The voltage regulator is bad or the Stator. Check to make sure you do not have something pulling power when the key is off.. Check the voltage should be 12.5 to 14.0, if it is lower then 12.5 with the engine running at idle. Check the stator for ground if the stator is grounding out bad Stator. If not, bad voltage regulator