Carging a battery with a charger.

Now this may seem quite a stupid question from someone with 45 years of motoring behind me but here goes. I have not had the need to charge the battery on my 2009 Passat other than drive it. Today it was cold and I felt, rightly or wrongly, that it sounded a bit flat. Not the usual zap. So can the battery be charged on the car with a automatic up to 8 amp charger or does the battery need disconnecting to avoid damaging the electronics and alternator? Will the car & radio need recoding if the battery is disconnected?
I cannot find the answer in the manual as it states that the battery is managed. (whatever that is). Any help appreciated.