Seriously though that is a question that is impossible to answer without knowing the answer to hundreds of different questions. Such as what is the size, make, and capacity of the battery? Is it brand new or 5 years old? Does anything you intend to use have a heating element of any kind, such as a camp kettle? (A definite no-no) What lights will you use and for how long? Ordinary bulbs use far more than LEDs. There are loads more.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.