1. Is it the Original Engine Battery? - can't tell as we bought the van 6 months ago and it's 9 years old - obviously can't be the original but the service history we have doesn't include batteries so we don't know how old. I shall pop round to out friendly local tyre and battery man and get him to test the battery, but I'm trying to gather as much info as possible before doing that. I think it may well need a new one because......... (see answers below)
2. Did you switch OFF the cab lights, that operate everytime you open a door? Switch by drivers mirror. Yes, I usually keep them off for that reason.
3. Did you use your Dashboard radio frequently? That runs off the engine battery We only used it for an hour or so
4. Do you have an electric sliding door , not just the electric latching? Yes we turned that off too!
If it is the original engine battery then it may not be able to store much of a charge and using 2 & 3 & 4 above may have taken it down sufficient.
Another possibility is:- The Cigarrete lighter 12v socket in the dash/cupholder/tray runs off the Engine Battery. Was this in use? No, I use it for the satnav but that gets unplugged as soon as we stop.
There have been reports of the 12v socket on the kitchen unit, behind the Passengers seat, being mis-wired to the Engine Battery. Did you use this?