The Addicks have shrugged off their poor start to the season and are now unbeaten in their last five matches.
Saturday's 1-0 win at Birmingham was also their fourth clean sheet in a row, and Powell revealed their new-found defensive solidity has not come about by accident.
"Things can change quickly, I understand that, but what we needed was a foundation," he said.
"So we worked hard. Sometimes it can be boring doing the repetitive stuff but it gets ingrained into them. The players have been brilliant."