The first Elite 4 isn't hard with the right strategy (I haven't done the second one yet). My Pokemon were all level 50. Just make sure you have Pokemon with the right attacks to take them down quickly. That way you can save your strength and items. My main suggestions would be to have a strong Electric, Psychic, and Ice Pokemon(Lapras is really good) and to have some Elixir/Ether handy so you don't run out of PP on a good attack.