What level air balloons operate as defense in addition to offense? Is it level 6? Would this be true for all characters; like dragon or minion need to be up to level 6 for defense?
Troops in your army camps are only for attacking, not defending. If you would like to have troops defend your base, you can repair your clan castle and join a clan. Once you have both a clan castle and a clan, you can request troops from your clan to defend your base. These troops will continue to defend your base until they are killed by an attacker, or you use them for attacking.