2002 Quest loose connection at battery

[tetal]

When I try to start my car I get no start/crack. I thought it was the battery and at first I would jump my car and it would start, but this would continually happen. I check the battery voltage when on and off and the battery/ alternator are fine. I narrowed the problem down to a pair of connectors in the below picture. It seems that during the operation of the car the connectors become slightly loose, however, the connectors don't appear or feel loose, but I still push the connectors in. When I do that the car starts up as usual. The two connectors that are connected to red part go to the fuse box. Should I replace the red part? Or try to clean it? Or is this a sign of another problem?