Why did your friend allow himself to be detained and interrogated by the TSA for several hours? He should have flipped them the bird, demanded his stuff back, left the airport and immediately called his employer's legal department. He was under no obligation to answer their questions once it became clear they were going to make a big deal about his tools and batteries.

They cannot detain or arrest anyone - the TSA is powerless to arrest or detain people, only law enforcement can do this, and they can only do it by arrest.

TSA managers, especially those on power trips, feed off the fear and deference given them by passengers who should otherwise tell them to buzz off and call for the airline GSC to intervene and witness any discussions which could impact the customer's ability to fly at that time.