Why does car battery and caravan battery go flat

Flat plate batteries have six sets of plates with glass mat separator containing the electrolyte are arranged in a straight line inside the battery. Because the plates are compressed in rows, the battery has more capacity, that is it uses all of the surface area inside the container to provide more energy when it’s needed.

All that is required is a cheap digital Meter. Measure the voltage when you stop, and before you connect to mains.

Unhook the NEGATIVE side of battery and put a test light between the batt and cable on the negative side if it lights up you have a draw on the system. On the motor home they make trickle chargers to hook up why you are not using it. On the first if you do find a draw usually it is a bad overhead light. if not unplug fuses till it goes out and then you know what system is drawing the battery down.