You would also want to clean out the brush holder or probably replace the brush assembly if the brushes are damaged
. The slip rings too should be cleaned by spinning the rotor with the hand. You must use a find cloth to get proper cleaning done. You would need to solder the connectors and also put the brush holder back in. An alternator which is an A/C generator can charge better even at lower RPMs which is why they are preferred over DC generators. In a vehicle, an alternator problem could be diagnosed through some standard procedures although you must be careful as the symptoms could as well be pointing to a bad battery or bad started. By disconnecting the battery cable you can replace the alternator in a vehicle too.