Powell, who replaced Phil Parkinson at the helm in January, got off to a flying start with four straight wins but seven defeats from their last nine games has seen the Addicks slip way off the promotion pace.
Writing in the programme ahead of Tuesday night's draw against Southampton, Slater said: "Chris Powell is a manager, not a magician, and I have publicly acknowledged that he did not have the ideal platform upon his arrival.
"In the months to come, Chris' work with the players will be complemented by investment in the squad so that, sooner rather than later, we will be capable of producing the sort of consistent performances we all want to see - performances that will see us push for promotion."
Source: PA
Source: PA