Walmart battery in my Honda Civic Toad

[Harvard]

About 2.5 years ago I installed a Walmart sourced battery in our 2007 Honda Civic Toad thinking it should last a few years. Of late I have had 2 separate incidents where the battery went flat while just sitting in the driveway for 2-3 days.

My question: Can a (faulty?) car battery just go dead like this (2-3 days sitting idle) without having any apparent load?

I replaced the Walmart battery yesterday with a genuine Honda battery so time may answer my question.