Charlton were thrashed 4-1 by University College Dublin in their final pre-season game in Ireland.
Young striker Karlan Ahearne Grant scored a late consolation goal as the Addicks were well beaten.
Valley boss Karl Robinson pointed out his team’s hectic schedule, which could have played a part in their two defeats in three days.
He said: “Don’t forget, we flew in at midday on Monday, we played that night and then had that long journey to Limerick to play a team who are in the middle of their season.
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“We got back at 2am and got up to play against a team who are also in the middle of their season.
“There’s a difference to being fit and trying to get fit and that’s why we’ve come here. We’ve come here to push ourselves to the limits.
“I’ve been coming here for a number of years and we’ve usually played reserve and U21 teams, but because of the way the fixtures have fallen this year, they’ve all played their main players and that’s made it better for me.”
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