Dell XPS 13 battery drain in sleep - probably found solution

I know this is an issue for many users and it was for me. I probably found the solution, at least the problem is fixed for me.

It pretty much looks like not the Intel stuff is the problem but the WiFi that keeps the machine up.

Go to

Control Panel\Network and Internet\Network Connections

Right click the Wifi adapter and select "Properties", then "Configure" and uncheck the box under "Power Management". Reboot.

Fixed everything for me so far.