I've had a few 'battery flats' over the years but the one I had two days ago reset my Control Head to some sort of factory default!
When I got the car started, the MMI and DIS text were in German and a lot of the options on the MMI Setup screen were missing.
Using VCDS, I discovered that the Control Head's 'Coding' was reset to 0000000 [a non-valid option] and some or all of my Adaptation channels reflecting my car's options had been reset.
Sadly, I'd never taken note of the channels [there's a VCDS option to do this], so I'm struggling to get all the menus reset to reflect what I've got in my car. [I obviously know the coding from AutoScan output that I've kept, although it only really selects the language - UK is '2'. I didn't realise that the ECU's adapation values could ever get reset, so I never bothered to save the values for my car].
Thus; if you've got VCDS, you might like to dump your CH adaptation data to a .CSV file while you can.
Julian