How long can a bat hang upside down?

Bats can hang upside down for as long as they want. They do not need to use any muscles to hold on to something. They have special tendons in their feet that lets them hang around without exerting any energy. All they have to do to hang is relax. The weight of the upper body pulls down on this tendon and causes the talons to clench or grab hold. The talon joints lock and the bats weight keeps them closed. The bat only needs to release its grip to fly off.