Shield drainer evasion
From Halopedia, the Halo wiki
Start the Armory on any difficulty. Go through the orientation process until you reach the recharging energy shields station. Once the "Hold A to start energy shield test" appears, navigate around to where the Master Gunnery Sergeant is standing. When the message appears again, activate it. Strangely, John-117's energy shielding will still go down even though he is not in the energy draining station.