Heat followed by Vibration are the 2 main killers of batteries, so if you had the hood up and the battery was in dirrect sunlight all day and a bit older I can see it. direct sunlight temps aren't horrible but if the battery is about 2-3 years old its def possible.
Matt, all I do all day is diagnose sell and repair batteries... for the last year and a half. I know my ****. Everytime you share your knowledge about the situations on them you are right on the money especially compared to the hear-say that other people toss in as if it were a proffesional opinion. Flattery nothing, there's right and wrong, and you are consistenly right