I know the good folks at Wal-Mart tested the battery for you and it tested good, but no harm in taking the battery to Pep Boys, NAPA, Checker Auto Parts, or similar place. Maybe the guy at Wal-Mart was new. I think it's noteworthy that the power center indicated a dead battery, and the indicator on the trolling motor only registered 1/3 of a charge - that means it's 2/3 depleted. I think that may be a clue worth chasing down.
If you registered a full charge, and the trolling motor had no power, then I think the prop would be the logical next step. I also think that your trolling motor needs to indicate a fully charged battery or you may be just spinning your wheels. I've never owned a Minn Kota Power Center, so I might be all wet, but can't you remove the battery from the power center and hook it up directly to the trolling motor? That would certainly help the trouble shooting process.