New Redemption Grab Bag now includes an assortment of 500 cards from five (5) different expansion sets. Available at Cactus website.
Special abilities default to play unless they specify otherwise (or have a default condition specifying otherwise such as banding). Gates doesn't specify otherwise so the demon added to battle must come from play. While it might end up being a band ability if there is already an EC in battle, add to battle is a distinct, separate ability (as far as I'm aware) with different default conditions.
I would like to at least keep banding from hand a legal play. I believe there's a great deal of strategy in being able to band in a "surprise" character from your hand.
Any ability that adds a character to a side of the battle where at least one other character is present is a band ability.
Default Conditions Targets must be in a territory or in holder's hand.