1---Very first thing is determine if the charging SYSTEM is actually charging. Stop thinking of throwing parts at it
2--Second thing is determine if there is a drain on the battery when the car is parked
A--Charging system---What does the ammeter do when the car is running? On a healthy system, immediately after starting, and with the car running on the "fast idle" you should show an obvious charge on the ammeter. Depending on how long you cranked the engine, the ammeter should gradually drop back to center.. Turning on lights, radio, heater blower, should result in the needle possibly fluctuating momentarily, and immediately going back to where it had been just before
If this does not happen, post back
B--Battery drain. Get yourself a 12V test lamp and a multimeter. If you don't have a meter, get one with at least a 10 AMP current scale. Some meters don't, and only measure up to say, 200--250 milliamps, about a quarter of an amp
Remove the battery ground, and put the 12V lamp in series from the battery post to ground. A battery drain will light the lamp to some degree, you may have to do this in reduce light to see the lamp glowing. Go around the car, look carefully, and make sure everything is off, the doors closed, the trunk and glove box lamp off, etc.
Post back here with results.