My understanding is Engine or motor it is, and I thought Turbo also is part of it, batteries might not be.
I was looking at the video from SkyTV about the Mercedes Turbo being divided in 2 basically with the compressor turbine in the front, and how much space and all the benefits it brings, but, McLaren is bulky in the back in contrast to the Merc car. So that brought this question. and if Turbo is the same why so bulky? also the radiators on the Merc seam so much smaller.
Video Link here: http://youtu.be/NuBB2F6IutQ

On the image I over imposed the Merc and the rear wing and inlet coincide so it is not just a matter of perspective, the Air Inlet of the Mercedes is so much shorter.
I cna't see the tubes for inlet and I don't have that much knowledge so, maybe you guys can find out more in the pics than I do.