Battery charging and discharging issues

Can someone please advise me on some issues.
Firstly we are talking about a 10 year old vehicle battery in a vehicle that is normally on hook up and smart charger when at home, so I know that I am on borrowed time with the battery.

1. When on hook up without the smart charger, either at home or on a site, does the Sargent unit provide any charge to the vehicle battery or just the leisure battery?

2. Twice in the last six months I appear to have switched off the ignition and failed to turn off the dipped headlights  before doing so. On both occasions the van would not start, it just kept on clicking when the ignition key was turned. The last time was last week after possibly only 4 hours when parked up. Is it normal for this to happen after such a short time or is it just another sign of an old battery?

3. On both occasions I was 'lucky' to have someone close by with a set of jump leads. Having done this twice I then read that doing this can possibly damage electrics in the van. Is this true? If so why does Peugeot show how to use jump leads in their handbook?

4. On my previous van, a 2006 Peugeot based Compass I seem to remember replacing the battery by simply undoing it, installing the new battery and connecting it up. No problem. Now I read about people attaching an extra battery to avoid losing vehicle settings. 

We have only had the van for 10 years and we always seem to find something new. On our recent trip to the isle of Mull and Ardnamurchan I found out how to turn on the follow me home headlight function when I slipped and caught the headlight stalk. Life goes on it just seems to get more difficult.

1. The on board charger will charge which ever battery is selected on the control panel.

2. Head and sidelights will use approx 10amps, so for an old battery with reduced capacity, 4 hours to drain to no start is not unusual.

3.If you follow the Peugeot procedure, jump starting should not cause a problem.

4. Don't know if Boxer can sustain battery removal without loss of some functions, ie radio code. MB Sprinter it is no problem not using a back up battery.

if I switch off ignition without switching off lights, the lights go out anyway, same van same age.

Thanks for the responses. The van is indeed a 2011 model. 
The Sargent unit is an EC155. It is not something I have really looked at. Having now done so I see that here is a fuse allocated for the vehicle battery, so I presume that this does provide some charge to the vehicle battery, possibly only at a battery protection level.
I would have thought that by switching off the ignition the light switch would automatically be switched off. I habitually switch everything off, lights, radio, heater fan when stopping but last week when the van would not start I realised that I had left the light switch stalk in the dipped headlight position and therefore, very possibly incorrectly thought that this may have been the cause of the problem.
I am unsure how I can direct the charger to charge a particular battery. I understood that the selection button on the EC51 control panel allowed me to select which battery to power the leisure equipment in the conversion.

Whichever battery is selected on the control panel is the one that receives charge from the PSU charger (EHU connected only). The amount of charge is dependent on usuage of onboard 12v items.

Thanks for that.

Therein lies my worry. If the light switch is left on and the ignition switched off no lights show. 
I was wondering whether any drain would be experienced with the ignition off but the light switch left in the on position.
However now trying to be logical I have switched everything off and disconnected the van from hook up. I shall leave it for possibly 4 hours and see what happens then. Following that I shall do the same withe light switch in the on position. 
I am not actually keen on trying to run the battery down but it does seem one way of trying out the possibilities.

The plot thickens. Methinks I need an electrician.
After five hours without anything switched on and no hook up, the van started well enough. At this point I tried the light switch and noticed that without the ignition switched on the green lights on the instrument console were on. I checked outside and the sidelights were on. I tried the dipped beam and these worked. I switched all lights off and tried to start the van. Not a chance, only the clicking noise that has been there on both previous occasions when it would not start. 
 I have put the van on charge and will give it an hour before trying again. 
The van is booked for a service in early July and I can bring it up then but do wonder if that is like giving Peugeot a chance to spend a lot of time, cost me more money than I care to think about and still get nowhere
Any electricians or otherwise out there with any ideas?