MJOLNIR power supply control unit
From Halopedia, the Halo wiki
The power supply control unit is integrated into the miniature fusion reactor located on the back of the MJOLNIR suit. It provides power distribution to the suit's functions and can be overloaded when too much power is allocated to one function or all functions for long periods of time. An example would be overcharging the shields, getting them drained, and then recharging them over a sustained period, such as when John-117 fought the overwhelming Flood for days during the Battle of Installation 04. While fitting the Master Chief with new armor on Cairo Station, an unnamed gunnery sergeant suggested that the power supply to his suit had sustained heavy damage from his use of it. Additionally, Cortana had used the power supply to power a jump using Halo's teleportation grid that she suggested wouldn't cause permanent damage to the power supply. This likely contributed to the damage his power supply had taken.
Destroying or disabling the control unit will instantaneously render the armor inert. This was demonstrated during the crisis on Gao in July 2553, after Special Inspector Veta Lopis detonated a small explosive she had placed in the power supply control unit of Frederic-104's Mjolnir armor, leaving the suit entirely without power.
List of appearances