Standard GS Teardrop equipment has no leisure battery included. That means, the interior lights, USB or 12V sockets and maybe water pump would work from your car’s battery. But it is much more convenient when you have twice or triple more electricity power from 105 Ah leisure battery which will be fixed in the kitchen on the floor among the drawers.
Leisure battery is always charging from your car when you are driving. Special relay is controlling this charging process that your car’s battery could not be destroyed.
You can also charge it at home, at the camp-sites or anywhere you can find outside 220-240V electricity source.
Leisure battery is necessary for fridge, for heating system, for TV and is recommended for sink.
Also, if you go to the camp-sites where cars and caravans have to be parked in separate places then leisure battery is extremely convenient.