My baja SC50 scooter is broken again. what's wrong?

after fixing a proplem with the CDI on my red (formerly pink) baja SC50 scooter, i am now facing a problem with the charging circut. when the engine is idling, i am reading exactly 2.7V from the terminals that hook up to the battery (normal right?). as i accelerate the engine, the voltage begins to drop, 2.6, 2.55, and so on untill it reaches about 2.4v. also, when the engine is idle ing and i pull the brakes so the tail light comes on, the voltage increases to 3v (shouldnt it drop? shouldent the voltage increase untill it reaches the optimal battery charging voltage?) the engine is fine. in fact, it riuns great! the head lights, dash lights, indicators, horn, etc. work when the engine is running. the dash lights are LED and the horn is peizo electric so the voltage must be DC even though the engine has an AC stator, so the rectifier must be working and the voltage is high enough to power the lights. is the batt. charging circut broken? is it shorting out? what part needs replacing?