Do I need a leisure battery?

A commonly posted generic question but I've not found one that matches the lower ones detailed here so hopefully of use to others who have these if answers can be found...

I must stress that my only concern is for my caravan’s fridge operation but hopefully this will become clear.

I regularly (only) take my caravan to sites with 240v hookups so didn't/don't see why I would need a leisure battery for any purpose at all?

I don't know whether this is correct - my caravan servicer last week advised that if I don't have a leisure battery when it is hooked up to 240v the caravan's charger would be supplying the 12v to the fridge which would be abusing it...he advised I should have a leisure battery because the 240v supply should be supplying power the charger which would in turn supply/top up the 12v leisure battery to make sure it had sufficient power to provide 12v to the fridge because, long term, the caravan charger is not designed to supply 12v to the fridge or any 12v devices in the van.

This sounds reasonable but is it correct?

The real reason which prompted my posting here is that when he serviced my van last week he tested and verified, so he tells me and I strongly believe to be correct, that the caravan power supply lead (by the A frame of the van) which connects to any towbar power socket does enable the fridge to work whilst towing (and the car engine on of course!) i.e. it was not a broken lead but when I connected my car to the van, the fridge does not work.

 I don’t know how he did this nor do I challenge this but I know he did not connect my car’s towbar socket to the van and he has today stood by his test and I trust him.

 Very interestingly however when he learnt that I do not have a leisure battery he advised that I need a leisure battery for the fridge to work whilst towing.

 So…I now have these 2 questions which despite tons on googling I cant resolve so can anyone help please?...

 1. If you only attend caravan sites where you hook up to 240v power and wish to use all caravan electrical appliances, do you need really a leisure battery so that the caravan charger is not damaged over time or is that incorrect?

 2. Can the fridge only work when towing providing you have a leisure battery?

 If 1 is ‘yes’ you might wisely chose to /must install leisure battery but if 1 is ‘no’ but 2 is ‘yes’ you might only decide to install a leisure battery if your journey time is so long that the drop in the fridge temp is unacceptably low?

Thanks sincerely in advance.

Ben