Car battery draining

check to see if it is charging or has a parasitic draw on it. most places check battery for free and charging like auto parts. also, check fusible links for alternator as well as belt and tension-er as recommended replacement for belt and tension-er is 60,000 miles or five years. See link for parasitic draw.
https://www.2carpros.com/articles/car-battery-dead-overnight.
Fusible link should have battery voltage both sides, it runs off of battery and is a red wire turning into black. Test at alternator.

I would start with checking the battery terminals and cables. If there is any greenish/whitish corrosion, then take them off and clean them off. A piece of fine sandpaper would work well for that, but they do sell a tool for it at the auto parts stores as well. Make sure that the terminals are tight enough that they cannot be moved around with your just your bare hands, if they can be moved like that and cannot be tightened any more, then replace the terminals. Also, make sure that the cables are similarly tight on the other ends.

If that does not take care of it, then you have an electrical drain/short somewhere in the system. You will need a voltmeter/multi-meter. Take one battery cable off. Connect one lead of your multi-meter to the cable, and the other end to the battery terminal. You should get some sort of reading on the meter. Then start pulling fuses until a significant change happens on your multi-meter (should be a drop in voltage). I always start with circuits that have aftermarket electronics on them (like that radio, for example). When you see that change, you have identified a circuit that is drawing power and should take a closer look at it to make sure that no switches in that system are left on, that there are no bare and exposed wires, etc.

You can also check out this guide: https://www.2carpros.com/articles/car-battery-dead-overnight

But I like my way more, personally.

You can also swap the volt meter with a test light. If it lights up with everything turned off you have a draw on the system. Start by pulling circuit breakers until the light goes out. Now look for the problem.

There is always going to be some draw on the system. The trick is finding the big one that is draining it overnight. Hence why I would use a multi-meter on it.