An Iv battle involves going into battle online with a friend to check your pokemon's Ivs. Normally, your pokemon would be at level 1, but because of the online feature that allows you to come into battle with all of your pokemon being at level 100, Iv checking was made easier this generation. The stat calculator that I had linked you to will help you with your Iv checking, but first, it's up to you if you want to check your Eevee's Ivs now. It will be pretty fast, and it isn't hard at all.