Just went out to the garage to take her out for a spin and the battery is flat. Now on trickle charge so no driving for a while. 
I haven’t used the car for about three weeks, but should the battery really go flat in that time; or am I looking at a new one?
Check that the boot wasn’t open or an interior light, and draining the battery - I did that recently and it only took 4 days for the battery to go flat.
If the battery decharges quickly again, then it could be the alternator.
Nope, just checked that and boot closed, light switched off.
Just started her up OK so battery must be charging OK, I’ll leave it on trickle charge overnight.
Now however the DSC OFF light is staying on, if it’s not one thing! Hope that is a simple battery related thing rather than an expensive repair, anybody know?
First, make sure you have the radio code. disconnect the negative terminal on the battery and check for dark current. Everything electrical on the car off. It should be no more than 20 milliamps, ideally around 15 milliamps, if greater than this the cause of the drain must be found. remove the fuses one by one until the current drain drops, the circuits controlled by this fuse are the cause of the problem. Favourites are the interior and boot lights and the radio.
Regards Geoff Peace.
I had the same. Found it was passenger door not properly closed.
I had DSC light on when I had recharged, but it went out as soon as I took the car up the road. Obviously needed movement to clear the fault.
Regards
Jim
Same here, battery flat after leaving boot lid ajar, recharged, DSC light stayed on, took for run and off it went.
For info, to clear the DSC OFF lamp after a flat battery, with the engine running you should turn the steering wheel to full lock one way then full lock the other way, switch the engine off then restart. The system has to re-learn the steering angle position sensor.