My Fiesta ECOnetic's engine fan ran its battery flat last night. Why? (And how to jump it in the future)

[Haza.]

So as the title suggests my 2009 Fiesta 1.6 TDCi ECOnetic ran its battery flat last night after a shift of pizza delivery.

I noticed the fan running for a while after driving. It had happened before, where I waited about five minutes before it turned off, so I assumed this would just be the case again. It wasn't, and now my battery has gone flat. 

I am having someone come look at the car in about an hour so I'll hopefully be able to start it up later, if the battery isn't completely dead. 

My question is, how could this even happen? I bought the car about 2 months ago, and had it checked by my local mechanic to which he proposed no major issues aside from some worn engine mounts. No fault codes either. So I don't understand what the problem could be. I am aware that the air conditioning is also non functioning if that helps with anything. 

My coolant and oil levels seem perfectly fine. 

Is there any manual way I could prevent this from happening again in the future before I figure out a permanent fix? 

My other question is, how do I properly jump one of these cars? I spent some time with a friend this morning trying to jump the car to no avail. I initially followed some instructions online which suggested I connect the black wire to both negatives, and tried to jump the car. Looking at other instructions, they says it's dangerous to do that, so I followed different instructions which asked me to ground the wire. Is it possible I've killed the battery?

Afterwards I followed the instructions from what I knew as correct and nothing seemed to happen. I'm unfamiliar with the engine of the Fiesta and wasn't sure exactly where to attach the second negative to ground it. It looked like there was a ball attached to the engine block but again nothing happened so I'm not sure. 

If there's any other information that could be helpful please let me know and I'll provide as many details as I can.

Thanks.

[TomsFocus]

The car is probably trying to do a DPF regen but failing because of all the stop/start on a delivery route. 

That'll keep the fan running on high speed while driving, and then after switch off for a short period of time as well.

The fan shouldn't run endlessly after switch off so there may be another fault there, or maybe the battery was already on it's last legs and a few minutes of fan has killed it.

You are correct with the jump start procedure - red to red on both batteries.  Black on the donor vehicles battery.  Then ground to a thick, solid piece of metal on your car.  The little ball on the engine was probably the mount for the engine cover, that may not be a thick enough piece of metal for this job.