I have a 1983 Honda aero 50 scooter with a new battery but it keeps going dead how can I test charging system?

I have a 1983 Honda aero 50 scooter with a new battery but it keeps going dead how can I test charging system?

Buy a cheap multi-meter from Harbor Freight Tools (about $10), set it to the DC 20 volts setting and measure the voltage across the battery with the engine running. A well charged 6 volt system (3 battery cells) should read about 7.5 volts running. Turn the engine off and it should still read a little over 6 volts (6.5 or more). If it reads the same off and running, the alternator is not charging. The problem is usually in the diodes that change the AC voltage generated by the alternator int DC voltage the battery uses. If these diodes start leaking in the wrong direction, your battery will go dead overnight. One way to check for this is to disconnect the negative cable from the battery when you turn the engine off, eliminating back-drain. If the next day you hook up the ground and the battery isn't dead, this is the problem.