Motorcycle Repair: Starting Problem, honda nighthawk 750, battery voltage test

Question
I have a 1982 Honda Nighthawk 750 which I just replaced the battery in.  The bike ran great for a day, but now the battery is dead again.  I looked at all the connections and they look alright, but the battery will not hold its charge.  When you jump the bike, it will run great until you shut it off, but then won't start again.  Because of this I don't think it is the alternator.  I have been told it may be the rectifier, but I'm not sure exactly what that does.  What is a good way to figure out what the exact problem is?  Is there anything else it could be? Thanks!

Answer
Emily,

-It is possible you are getting some charge
but maybe not enough to keep the battery fully charged.

-Borrow or buy a multimeter to check
the battery voltage while the bike is running
about 2 or 3 thousand rpm. You should
have between 13.5 to 14.5 volts.
Anything lower is not enough and means
your stator is faulty or your regulator/rectifier.

-Try checking any connectors going to the engine
and check your fuses.

-the stator usually has at least 3 wires of the same
color coming from the engine.
The voltage between any two wires should be 50-60 volts
in AC current. Also none of the wires should
connect to ground or the engine or frame.

-if the stator output is good, usually the
regulator is at fault. Often poor
connections can be blamed as well.
The regulator converts the stator output
from AC current to DC current so it will
charge the battery. It also regulates
the charging voltage.

-if you think something is draining the battery
overnight, try leaving the negative cable
off until you are ready to ride,
see if it helps.
The battery voltage test should tell you if the bike
is charging though.