Leisure battery charging question

DaveandCarol94

Hi, we are new to caravanning and have recently bought our first caravan ( Lunar quasar FB), I was wondering how to keep the battery charged while in storage as when I popped over to put some bits in the caravan the battery was flat. I hooked the caravan
up to the car for about an hour while I made up the waste pipes and a few other jobs which has charged it up a bit. Any advice appreciated.