charge is a fundamental property of matter that is very difficult to describe in physical terms, you find electron , quarks etc have charge , but if you break electron or quarks ( which is a fool thing to say i.e they are elementry particle ) you are not going to find any separate thing...
this question is difficult as we use energy to define certain things and work , but on its own energy is a fundamental thing that cannot be physically defined exactly as you have to use few undefined quantities to define other things ( like Axioms ) , same as it is very difficult to define...
well empty space does not mean that there is zero energy , and as relativity says energy is equivalent to mass , and mass create gravity . hence if space -time is there then i think gravity is also there.