The Addicks have thrown away the lead to lose 2-1 in their last two matches, at home to Sheffield Wednesday and in Saturday's south London derby at Crystal Palace.
They led through Ricardo Fuller's first-half opener and had numerous chances to extend their lead, but could not take any of them and eventually crashed to Glenn Murray's late double.
"Palace couldn't really handle Ricardo Fuller and the way we broke from midfield, but you do need to take chances, even at this level," said Powell.
"We talk about the Premier League and one chance and it is in the back of the net, but even at Championship level you do need to take the chances that arise and the chances that you make. We didn't do that."