Hi, as your Alphard is a camper. the answer could be what I use,we have a camper conversion which has a 12volt hook up point and a 12v cigarette lighter socket.The socket and the cigarette socket can be used to charge each battery in turn using either socket with a 12v trickle charger[mine were purchased from Toolstation].These can be left on and once the batteries are charged will trickle charge as and when. If you have a 230volt hook up you can use that to charge the leisure battery via the 12v socket
I can only speak from my experience as I have,besides the camper,2 tractors,a Quad bike a lawn mower and shredder, each connected to one of these chargers and I haven't had a flat battery since using this method.I am now going to run leads via fuses from the main battery to an extra lighter socket in the dashboard area for trickle charging the main battery.
Hope this helps and your time in hospital was successful.