Used car V50 D 1.6 DPF, purchase decision, where does oil come from in the engine compartment

Hello dear forum, First of all warm greetings from Bielefeld! I am interested in a V50 D 1.6 DPF, 11/2007, Kombi, and I could already look at the xten. I would have liked to. 133tsd run, DPF, LM, battery, additive, inspection was made in November 2014. I noticed, however, that under the battery on the thing is an oil-dreak-sminder film. Have I seen now with some. And now I ask myself of course: What this comes from? AND: Does this have to be done? Maybe you have an idea and can help me further? Thank you! Judith