Muh240sx

I’ve searched all over for answers pertaining to this problem, and I hope this is in the proper section to get help, but basically as the title says, my car will die and refuses to start acting as if it has a bad battery despite me just getting a brand new one a month ago.

Basically I bought a used two owner 1989 240sx two tone coupe that?s been in a family forever for a okay price, and it?s got minimal rust. The car had been sitting since 2018 after it had gotten about $7500 dollars in repairs of just general maintenance like new lines and new undercoat.
Well it ran fine up until early November when after I had done some tinkering with the radio and speakers and my buddy forgot to unplug the battery while I was working on the cars radio, one simple job. Basically I noticed after that the car ran fine for awhile radio worked great and suddenly it just died, so I attempted to start it without the radio and I got it running for a minute before it died and acted like it had a dead battery, so first things first was to replace the battery, which I did, and to no avail. I drove it 30ish miles before in decided to start stuttering like it had no fuel or power and died, I got a jump from someone and it cranked right over, only to die not more than a quarter of a mile down the street. So I dropped the battery on the charger and hoped it would run fine which it did, for 20ish miles before leaving me stranded once again. So I cleaned the IACV valve, MAF sensor, changed spark plugs (not part of the issues just wanted to) cleaned up the throttle body and put a new battery in again in case I had a faulty one, and still nothing ran for 20ish miles again and almost died until i mashed the gas and it acted like it wanted to die but it kept going, wouldn?t go over 5-7 miles an hour until I got it home and it?s been sitting since. I?m confused on what to do, and really want to get it up and running as I want to store it for the winter, but I?m having no luck deducing anything.

Thanks again for any suggestions if you guys can toss any my way