What needs fixing if the battery and alternator keep dying?
I have a new battery , I have a new alternator, I have a new belt - what do I fix next?
You need to check the voltage output. Your output should be between 13 and 14 volts when car is running. You can contact a mechanic for more troubleshooting options.
either something is staying on...for example, glove box light, trunk light,.etc, or...you have a short in the electrical system.
All other answers are good but also keep in mind a new alternater doesn't mean it's any good. Many new car parts don't work. Hope you kept the receipt.