I have a 2015 Golf whose battery needed replacement. I noticed that the battery tray was designed to accommodate three different lengths of battery, with the factory battery being the shortest (and smallest) possible. So, in hopes of having the replacement battery last longer, I got a larger battery.
Problem: the factory battery had a sort of a box wrapped around it, made of a folded sheet of black fibrous material. The material was puffed up in thickness, as if for thermal insulation:
It don't make sense that the box is for electrical insulation, as protecting more than just the terminals isn't useful. It also doesn't make sense it's for thermal insulation, as no matter what the battery will eventually get to the temperature of the surrounding engine compartment. Maybe it's "just for pretty"?
So, what is this box for, and do I need to replace it?