It doesn't use up my two charges when i play. But if you melee someone else it does burn up the second charge, even though you already have force barrier up. Get the immobius shotgun. Melee for force barrier then shotgun in WoD till your force barrier runs out. By the time the second barrier runs out the first charge should be back. Sadly though it does prevent you from meleeing multiple times without wasting the second charge.