Battery keeps draining

hey guys sorry about the delay! Im still here, ive just been brainstorming and fixing everything i can before winter hits!, well , as for the battery, it did it twice, and never again. I had contacted the previous owner and asked him when he bought the battery and he told me 4 years ago. So chances are it was just a cruddy old battery being weird... Thanks for the help though, ill probably end up just replacing it rather then test it considering its age, what do you guys think?