Hi I am a total campervan novice, I have a 2005 2.4 Alphard & had this problem last year with the doors & twice the battery went flat. It had a new battery fitted when we bought it the previous year. Mine also is not used every day & on these occasions had been on the drive several days. Charging the battery sorted it out & our mechanic suggested we buy a ‘trickle charger’ device to stop it happening. Haven’t really looked into it yet & not had any problems this year yet but now make a point of going out more in the van especially as it’s getting colder.