You have several possibilities:
1. bad battery
2. no, or low stator output and/or bad rectifier/regulator
3. high parasitic drain with the key off
I would troubleshoot this way:
1. Verify the battery with a loaded test (once it has fully charged). Only a loaded test can properly verify the battery. Battery shops can do the test.
2. If the battery is OK, connect the battery and measure charge voltage while the engine runs. It should be >13.6V at 3000 rpm and <15.5V. If the voltage is too high or too low, check the rectifier/regulator.
3. Test the parasitic drain with the key off by disconnecting the ground lead to the battery and measuring current between the ground lead and the battery with an ammeter. It should be just a few milliamps or less. If the parasitic drain is high, check your aftermarket accessories first (by disconnecting them). If parasitic drain is still too high, unplug the rectifier/regulator to see if the high drain current goes away.