Hoping I can help someone as the battery drain on my MK5 FSI took years to resolve. Ended up being the Fuel Pump Control Unit which sits on top of the fuel lift pump under the back seat. Cost about $50 from memory and is a simple swap. I only noticed it one night when sat in car whilst in garage and heard a very low level buzzing from the back seat. I think the primer pump kicks in on door opening to push fuel up the line and should only be on for a few seconds, but it was constant. Pulled the fuse to the pump and issue stopped. But its was intermittent and could go a week or two with no battery drain. So if you're looking for an option to fix a battery drain maybe just pull the fuel pump fuse out at nights for a couple of weeks and see if pain persists. Goodluck.