Anyone have any experience with this issue?

My rear fog light bulb occasionally turns on - it is usually around bad wet weather..  the only way to fix this is by taking the bulb out leaving it a while and then you put it back in it seems fine. I took it out yesterday morning- didn't put it back in and this morning the battery was flat.

 

nobody else seems to be able to help

Hi Sean and welcome to the forum. 

That's a strange issue you have. Your rear fog light develops issues in bad weather. To mevthat smacks of a leak through a seal and it's wrecked the contacts inside the fog light unit itself. I suggest replacing the whole unit with a new one. Make sure the seal between the glass bit and the unit is sound. 

It's quite probable that corrosion has caused a short and that's flattening the battery.

1 hour ago, Sean30 said:

My rear fog light bulb occasionally turns on - it is usually around bad wet weather..  

The operation of the rear fog light on your car is controlled by the Body Control Module (BCM) which is part of the passenger compartment fusebox located behind the glovebox.

In many similar cases the problem is water ingress to the BCM which causes a fault. On a 2015 model it's not so common as it was on models just a few years earlier but it still needs to be checked. Before beginning work on checking the connectors of the BCM, first disconnect the negative lead of the battery.

Ideally you need to remove all the plugs from the BCM and fully check for signs of corrosion and/or water ingress.

Good shout. I didn't think of that.