Ok, I have the readings...
Just to recap, my battery light is always on and so is the abs trifecta.
My battery died on the drive the other day but I think it was because I had the doors open for 4 hours whilst changing the carrier. It's since been on a trickle charger.
Battery was dead 11.2v
Charged up to 13.16v
After first start 12.53v
After 1 hr with battery disconnected from car 12.6v
Started car after 1 hr, idled at 13.8v
Revved to 1500 and got 13.92v
car is now idling between 13.8 and 13.85v

I don't see what is wrong? These numbers seem ok yet my light is still on. Any ideas?

You really didn't follow through on that battery test properly. After charging, (via charger or driving the car), disconnect the battery and let it sit for at least two hours, three would be better. One hour is not enough. Then test it with a VOM, not by hooking it up, starting the car and looking at the voltage in the cluster. But the 12.53 volts you got seems a little low, but without the proper test, there's no way to be sure. The minute you start the car, your alternator bumps the surface charge up on the battery, quickly overriding any juice you used starting the car. The problem is that the surface charge will give you a false high reading. A good battery tester will not be fooled by the surface charge. But if all you've got is a VOM, you need to deplete that surface charge fully before testing.

It doesn't have to be this complicated. Just get the battery load tested. The alternator voltages are in the normal range.

Ok, I'll do the test again. Just for info before I put the charger back on I got 12.44 volts, that was after the car was left overnight connected to the battery. Anyway, I'll stick the charger back on now...

bcredliner - I appreciate your comments but im not in the US and I do not know of any places that do load test, nor do I trust the garages around here hence why I would like to perform the test myself and also learn a little along the way. I get that I need to test the battery but at the end of the day, isnt it the alternator that influences the battery light, not the battery itself? In saying that, I know that I need to fix the battery issue if indeed it has a fault. Please keep your comments coming - I'm determined to get this issus sorted.

Assuming you have an acid battery, 12.44 volts is only about 75% charged. So if you get it to 100% on the charger, and then take off the charger for several hours, and by itself, without being hooked to the car, it goes back down to 12.44 volts, it may not be a totally dead battery, but it's NOT fully right either. Perhaps a dead cell. After sitting for at least several hours, (but better to test first thing in the morning with no charger on all night), and dissipating the surface charge, it should test 12.70v+. If doing this test repeats the 12.44v, replace the battery. You may still have other problems, but these cars are so particular about having a good battery, that it needs to be done.

Also, just to note, unless you have a deep cycle battery, (generally used for marine use), every time you drain the battery to the point where the car needs a jump, you have done permanent harm to your acid battery. Do that a few times, and it may not be up to snuff for a fussy electronic car like an X5.

Cheers Skyline, ill report back tomorrow once its charged and left over night disconnected.
I'll also look into the wiring at the alternator end, although I guess ill have to remove the fan / belts etc to get to the wiring? I also thought about testing the voltage on the dash - as per the earlier post.

I noticed you are not in the neighborhood. I am surprised that is not available to you as it is so common here. The battery 'stores' don't load test the battery to make sure it is bad before they sell you a new one?

Are you checking the battery and alternator voltage from the cluster or otherwise?

Did you clear the error codes when did the scan and they have returned?

You could buy a multimeter that has a battery load test option.