I've considered that it might be oils from my hands but the change is so uniform I can't see that being the case. If it were from my hands I think it would be more concentrated to the areas where I am more prone to hold it.
It's not a paint actually but some sort of protective coating over top of the actual paint it seems. I got frustrated and took one of the smaller batteries and scraped the discoloured layer right off. Now it's white as white can be, no more weird greyish colour, jsut some minor scratch marks where I accidentally peeled the paint as well as the top-coat.
I've attached a photo to show you what I'm talking about. They start out the same colour as the cartos - I left one attached so that you can see the progression. The one on the bottom is my newest, and also the least changed. The two in the center are the originals that came with my kit which is about 8 months old. The top one is the one I scraped the layer off of today.
