Here we freaking go again.
The car has been absolutely fine since my last post. Battery's been holding its charge at between 12.3 and 12.5 volts.
I get home from work this evening and the first thing I hear when I walk in the door is "the car won't start".
Checked the battery, it's down to just over 6 volts.
The car started and ran normally yesterday.
I haven't bought a new fan relay yet. I guess my previous theory may be out the window but I am still suspicious of the aftermarket anti-theft system as ten days ago the weird problems went away after I turned the system on/off a number of times.
Take a look at the attached picture and let me know if you think the droplets & dried whatever-it-is looks normal to you.