Charge up your battery again and then when fully charged and the car is off, disconnect the negative connection from the battery terminal. Use a multimeter and set it to amperage reading mode (usually moving the connector to a different spot and setting the dial to amps). Touch the negative connector with one of the multimeter leads, and the other lead to the negative side of the battery. The reading should be very low, under 0.1 amps at most. Hopefully closer to 0.05A or so. If it is above this amount, then disconnect the new alternator from the system. Test with the multimeter again and see if the current draw changed. If it has gone down to very low, the new alternator is bad. If it still has a high draw, then something else in the car is draining the battery. Do all lights in the car shut off when the car is off and you close the door and lock it?
If you have done the above procedure and ruled out the alternator, then find a way to make the leads of the multimeter stay in place. Usually, you can get multimeter leads with alligator clips on them that will help. With the multimeter in place to read amperage, go to the fuse box inside the car under the driver area. Take a picture so you know where everything goes. Now you can start removing fuses "smartly" by looking up what each fuse does and make educated guesses about which to remove first, or you can simply start with number 1 and work your way down. Remove the fuse, check the amperage draw. Still there? remove fuse 2, repeat until the current draw goes away. Once the amperage reading drops with the removal of one of the fuses, replace back all the other fuses besides that last one you pulled. Check and see if the multimeter still reads low amperage with all fuses but that one back in place. If so, look up what that fuse powers and you have your culprit.
Everyone *should* have a decent multimeter around for troubleshooting a variety of electrical issues around the house or vehicle, but sadly most people do not. If you need to buy one here are some options:
cheap basic unit:
https://www.amazon.com/AstroAI-Multimet ... 30&sr=8-14
somewhat good, average spec unit:
https://www.amazon.com/AmazonCommercial ... 470&sr=8-7
https://www.amazon.com/Extech-EX355-Pro ... 706&sr=8-6
overkill for what most people need:
https://www.amazon.com/Extech-EX530-Hea ... 302&sr=8-1
And if you get a decent one with bluetooth you can watch your phone as you pull fuses to see when power goes away.
edit: you will need to either find a way to keep the door switch pressed down while the door is open so the car doesnt turn its interior lights on, or just see what the reading on the multimeter is with the door closed and then see with the door open and mark down how much power the lights are drawing. If you leave the lights on inside then when finding out where the larger drain is from one of the fuses dont forget to take into account the lights being on for why the amperage hasnt dropped down to 0.1 or less.