Hi…Just browsing through my past contributions to the debate on battery chargers and thought I would add my experience to date, for what it might be worth. A few years ago, as a result of having a very flat, seemly dead, original Panasonic battery on our first 5, a W Reg, I bought a “CTEK Multi XS 3600 Battery Charger” as a result of an entry in the Forum on the subject in which a member recommended this “intelligent” device. There are other CTEK models in the range but this seemed ideal and adequate.The battery was completely revived and the new owner of the car, who lives local to us, is still running the car on that battery and is still speaking to us! …12 years old and counting!
Meanwhile, every winter when the roads get bad with ice, snow and the inevitable salt and grit, I couple up the CTEK in situ, without disconnecting the battery, using the supplied leads, which are permanently attached to the battery, and it ticks away keeping the battery in our second car (02), another original Panasonic, in tip top condition. Recently, I managed to leave the interior light on and was greeted a few of days later of non-use of the car, by a very very faint interior glow from the lamp.
On connecting up the CTEK I noticed that it did not stay on the car charging icon but moved immediately to the frost setting as the weather outside was down to 2 or 3 degrees. The battery was soon revived 
and, until I need to shut down for the weather, when it eventually comes 
, the CTEK will remain next to a power point I plumbed in and fixed on to a small board, ready for the period of hibernation, should it come.
Hope this proves of interest and possible value.