Battery seems to have died 
I know some on here use just the van battery and don't bother with a separate battery.
I want to monitor the van battery make sure I don't flatten it and get stuck etc..
What should I check for with a voltmeter.
The Amps the battery is putting out?
The Volts the battery is putting out?
Ta.
We weren't able to get the van's battery as a power source to work on two of our vans - we do very limited mileage. Even after we fitted a new van battery, the battery was flat after four days.
The voltage of the battery is what is checked to ascertain whether it is flat or not. However, the battery needs to settle down (equalise) before the state of charge can be accurately measured. A battery can also take on the appearance of being fully charged but doesn't have the capacity. So it may just start the van each day, but leave you nothing in reserve.
You could connect up to your van battery for a day and then put the charger on it at night. Firstly you will need to make sure that the van battery is fully charged. Our charger is an 8 amp unit and has a red charging light that turns green once the battery has been fully charged. If you put a charger onto your van battery now, it should very quickly kick the charger off or into trickle charge mode as it should be near enough fully charged.
Once the battery is fully charged then go out and do a days work. When you get back home, put that charger onto the vans battery and see what the situation is. If it needs a charge for a short time, then you could probably assume that you will be ok. I would then do the same experiment for 2 days before putting the van's battery back on charge, then try 3 days, etc.
If it takes a while to replenish the charge in the battery, then the alternator isn't keeping up with your current use and you will end up with a flat battery. (If you take more water out of the glass than you put back, you will end up with a empty glass.)