Battery keeps dying

You really have not included any test results, observations, or clues I can use to tell you where to start. Just so I am clear, when you say. "it wont start my car at all", do you mean the starter will not crank the engine? "Wont start" is also used to mean the starter cranks the engine just fine, but the engine wont run.

This guide can help

https://www.2carpros.com/articles/car-battery-dead-overnight

If that is correct, what are the additional observations? Are the head lights dim, then they get dimmer during the attempted cranking? Are they bright and stay bright during cranking? Do you hear the single, rather loud clunk of the starter solenoid when you turn the ignition switch to "crank"? What do you have to do to get the starter to crank the engine again?

Use a digital voltmeter to measure battery voltage, first with the engine off, then with it running. Tell me what those numbers are.

Something was lost in translation. You cannot get "0" from a battery. Harbor Freight Tools has a perfectly fine digital voltmeter for less than ten bucks. They often go on sale for as little as three dollars. If you do not know how to use one, I can help with that.

With the engine off, a good, fully-charged battery will read 12.6 volts. If you find close to 12.2 volts, it is good but discharged. If it is around 11 volts, the battery has a shorted cell and must be replaced.

With the engine running, the battery voltage must be between 13.75 and 14.75 volts. Testing for the solution to this problem has to be done while the problem is occurring. In this case the "Battery" light is telling you when the problem is acting up. You are going to find the battery voltage is back down to around 12.6 volts or less with the engine running and the problem is occurring. Lets jump ahead a few steps and measure the voltage directly on the large, bolted-on output wire right on the back of the generator. You should find the same voltage there that you do right across the battery posts. I suspect you may find a voltage considerably higher than the voltage at the battery.

If the problem presents itself before you get a voltmeter, and you do have a test light, put the clip on the battery's positive post, then probe the generator's output terminal. The light should not light up even a little because those two points are the same point in the circuit. If it does light up, check the tightness of the connection on the generator, and look for a bolted-in fuse in the under-hood fuse box. Be sure those bolts are clean and tight.