Hello, new member here! Our 2002 Alphard has a quirk, where once a month or so, unrelated to weather, it will spontaneously act as if the battery is dead. The clock resets, it won't turn over. However, I also can't jump start it. In both instances it started up again no problem about an hour later and it was as though nothing had happened. Any thoughts? 

have you look at your battery connections? Sometimes fouling or loose connectors will do this or the negative terminal from the battery to the van metal if its not earthed correctly will do this too.