Dud battery

[Heisenburg]

Happy new year to you all.

Just wondering if you guys can help with a few questions on the CSL's battery...

I've had the car tucked away for the winter and just got a CTEK 5.0. But I think I've been beaten to it as the battery is dead and I'm not holding much hope of resurrecting it.

- can you tell me what type I should looking for with a new off-the-shelf battery instead of going to BMW.

- I notice there are two vent holes on my existing battery (one next positive, and the other opposite at negative). My breather tube goes to the positive...can the negative one just stay open as is, or does it need to be plugged, or even its own tube?

- just going on from this, do you reckon it is safe to leave my CTEK connect over the winter with a car cover on. I imagine this will effect the venting?

- am I thinking way too much about this?

- and finally, can anyone tell me what the blue/red cable below is for (next the positive terminal)? It looks a bit lonely.

.

Cheers fellas

Paddy