The tricky winger spent three years working under the Spaniard at Anfield before making a switch to Spanish outfit Real Zaragoza this summer.
Pennnant struggled to hold down regular first-team football while on Merseyside, with Benitez renowned for his rotation policy.
The 26-year-old admits he grew tired of being prevented from playing his natural game while with the Reds, claiming he was unable to perform to the best of his ability due to the incessant demands placed upon him by his manager.
"When I was on the touchline all I could hear was Benitez giving me directions," Pennant told the News of the World.
"At times I'd think 'why don't you just put the batteries in and turn me into a robot'.
"Sometimes I just wanted to play my natural game, but there were so many instructions: how to go forward, how to defend.
"He has been through so many players, so many strikers, so many midfielders that he takes the best attributes out of them."
Pennant has also revealed that he endured a distant relationship with Benitez, meaning that he was never able to fully understand why he was overlooked on so many occasions.
FaithHe added: "I didn't understand it. There are players at Liverpool and you think 'how is he getting a game?', but Rafa has faith in them. He thinks some of the players are the best thing since sliced bread.
"Rafa didn't have confidence in me. I'd play one week, then I'd be out of the team and think 'hold on a minute - last week I scored one and made two. How does that work?'
"He can be cold, but that's his style. He has a special relationship with Steven Gerrard and Jamie Carragher - but that's because they are Liverpool. There were times when he took offence with me because he could see how frustrated I was.
"I don't know the reasons, but he's won the European Cup and you can't argue with that. It kills half of Liverpool that they haven't won the league for so long. Something can't be right and they need to start looking into it quickly."
Pennant is delighted to have broken his Anfield shackles after completing his move to Spain, and claims he has set his sights on forcing his way into the England fold this term.
He added: "The ambition is to get into the World Cup squad. I've never been named in a squad, but I've never given up hope. (Fabio) Capello has twice been a manager out here and if he comes to Spain he's only coming to watch one player.
"Ian Wright got into the England team when he was 26 or 27 and I know it can be done.
"My assets are pace, going past players and crossing. I don't think anyone in that squad crosses the ball as well as me."