To activate the Armor, the Digi-Rangers must insert their Crests into it, and then slam the part with the Crest and it allows their armor to be summoned.
When Dan gained the Battlizer, he gains a slight upgrade. It gains some of his Digivice color.
When Digi-Rangers are under Lilithmon's control, she summons the Digi-Armor, around them.
When the Digi-Rangers got the power of the Zeo Diamond, the Digi-Armor becomes obsolete.
Adam reappears, and so does his old Digi-Armor, when he and his predecessor Carlos are attacked, Adam becomes the Black Ranger again.
Adam reappears in "Once A Ranger", with his Armor repaired.