which marathon implant says that using an energy amp grants tactical and primary energy to crew mates
The implant is Energy Reservoir. It says: “Using an Energy Amp grants tactical and prime ability energy to nearby crew members.”
Quick Scoop
That effect appears on the Sprint Kit V4 head implant in the Marathon implant database.
It is also listed on Marathon wiki pages as the Energy Reservoir trait for head implants.
Plain answer
If you were trying to remember the name from a forum/build guide, the exact implant name is Energy Reservoir.