13 Pin extension lead

They're not something I've ever seen. Bare in mind though that when your car is connected to the caravan with its engine running, the habitation relay will disconnect the 12 volt supply to lighting etc

Can't say I've seen 13 pin extension lead but you could make your own up, there are plenty of drawings to be downloaded of the pin colours.

You can  connect van to car via such a cable, and, without engine running you can power the van from the car battery.  Best done only in an emergency.

To charge the battery in the van from the car would involve having the engine running, which is not likely to make you popular with other campers.

Best get a good solar panel.

Just made one up so I can check van before moving it from its parking space and hitching up. 1 male 13 pin plug .1 female 13 pin socket. 5 metres 13 core lead. total cost £35 . worth it for peace of mind.

Engine might well need to run higher than normal tickover speed to provide any real charging and there will be a voltage drop so any such cable should not be too long and should be thick.

20 years ago I generally toured without a caravan battery but the car was only powering lights and water pump and was driven daily. Did not have mains electrics either

Hi Robstix.KjellNN hits the nail on the head. Why would you want to charge from the car? OK - in an emergency you may want to or have to but I have not had to do it in 3 years plus. If I ever do, I will just hook up as normal.' Best get a good Solar Panel ' was the comment and I concur entirely. If you are thinking of going non EHU, the heart of the operation is a good (powerful) SP and preferably a Safefill cylinder(if you want to save money) As a starting point I would recommend 120w. I have a 135w and I will be fitting a 200w on my next van. The SP, if its got enough ummph, will keep your battery charged to the max. That's the next thing - a good battery. A 110ah battery in good condition will give good service for lights, pumps etc. I fitted a second 110ah battery. What's the point of making all that lovely free electricity if youI cant store it anywhere? So, you shouldn't really need a special lead - best spend you money on good quality non EHU kit. Hope this helps.

Hi Robstix.KjellNN hits the nail on the head. Why would you want to charge from the car? OK - in an emergency you may want to or have to but I have not had to do it in 3 years plus. If I ever do, I will just hook up as normal.' Best get a good Solar Panel ' was the comment and I concur entirely. If you are thinking of going non EHU, the heart of the operation is a good (powerful) SP and preferably a Safefill cylinder(if you want to save money) As a starting point I would recommend 120w. I have a 135w and I will be fitting a 200w on my next van. The SP, if its got enough ummph, will keep your battery charged to the max. That's the next thing - a good battery. A 110ah battery in good condition will give good service for lights, pumps etc. I fitted a second 110ah battery. What's the point of making all that lovely free electricity if youI cant store it anywhere? So, you shouldn't really need a special lead - best spend you money on good quality non EHU kit. Hope this helps.

In the bad old days I remember putting the leisure battery in the boot of the car and attaching a cable to it with alligator clips and driving around charging the battery that way.  I have probably still got the cable for it with a 7 pin plug hidden away in the garage.  I haven't even thought of doing that recently - I am far too old to lug the battery round like that (they are a good deal heavier now!)  As Merve and KjNell have said there are simpler ways of doing it that are more neighbour friendly too. 

Before the advent of blown air and now Alde I caravanned for 15+ years with no need of a battery for the caravan - never use a TV in the caravan except at Christmas. I simply used an extension lead to connect to the tow car on site. On a few occasions when having 9 days away near the coast I carried a battery so that when I drifted off site at 6am to fish a tide for a couple of hours the family had lights and water pump whilst the car was away. Similarly the last holiday that I had with my late wife we took a battery as although we were away for 7 weeks I had to pop back into work for 2.5 days or so. Didn't need to recharge it though as generally used the car. 

I agree though if you want more power to the battery rather than using car battery then a Solar Panel sounds a good idea

Before the 'invention' of EHUs and electricity in cvans, we used to run a TV in the van from the car battery via the old type single towing electric socket and a home made extension cable. 

These days I'd go for a SP if I was intending to be off EHU for more than a couple of days.