The Addicks suffered their second defeat in three matches last night as they came away from Craven Cottage without any points.
Charlton struggled to match their opponents in the first half as goals from Scott Parker and Hugo Rodallega put the hosts in control, but Peeters believes that they made a big improvement after the break.
"At half time we changed the system and there was only one team on the pitch," he told BBC Sport. "If we score we are back in the game, and we had more attempts on goal than in our last five or six games put together. Everyone gave their maximum in the second half but it's about scoring the goals and that is what we lacked."
Charlton continue their Championship campaign next Saturday when they welcome Sheffield Wednesday to The Valley.