Battery questions for a newbie?

so the battery that they gave me with the camper purchase is not a sufficient battery? so even if I never ever ever dry camp I should still replace these two batterys with another new battery? im not sure what the benefit would be for upgrading a battery that doesn't get used? I am trying to learn all this, so this is just a question so I know and understand.. I want to make sure I understand your suggestion correctly...thanks again.