Hi, I just bought a 2004 Mini Cooper S from a private seller. I was informed the car was well maintained by its last owner (whom passed away) and he would regularly take the car to the dealership where he bought it from to get it serviced and she has the records to prove it. However since the sellers dad passed away the car was sitting in the garage for a long time and thus she decided to sell it to me. She bought a new battery from Walmart 4 days ago and placed it in the car, it ran. I bought it and I took the car home yesterday, however as I was driving home some of the components of the car stopped functioning, including the window not going back up and radio turning off as I drove, eventually the car stopped. I had it towed and as it turns out during a battery test at oreillys, the new battery that was put in the car was dead already. Does anyone know what could have caused this and how I can get the car to begin running again? I am thinking about purchasing a new battery but I’ve been told there is a slight possibility it could be the alternator? I don’t think it’s the alternator because it seems the car was very well taken care of, however it has been sitting in a garage for almost 2 years so I’m not sure. Any help would be appreciated as I’m a newbie to British cars. I used to own a Japanese car.

(In short) just bought this car that was sitting for two years, put a new battery from Walmart in it and it will not start or make any noise with the new Walmart battery in it. I turned the key and engine was not even turning during ignition so and it didn’t make any specific type of noise whatsoever, car ran very healthy but died right in the middle of a highway at a stoplight.