You have to remember that these charging systems are AC voltage. A diode actually synthisizes DC voltage because it only allows currant to flow in one direction. Many times you will have a new battery and it keeps going dead. This is usually due to a bad diode because while it "WILL" charge, but when you shut it off, the bad diode is no longer allowing the currant to flow only one direction, so with engine off, the currant flows "FROM" the battery back to the alternator (like a motor) therefore draining the battery. B & S uses 2 different types of diodes. One is a one wire inline usially red and appears like a bulge in the wire. The other is a 3 or 4 wire module encased in epoxy. This is also a regulator. With a low battery it will allow full charging capacity of the alternator, but as the battery builds up charge, it lowers the output as to not overcharge the battery