The use of mobile manipulators for transport tasks has provided solutions to some flexibility problems in manufacturing systems. Mobile manipulators are mobile entities equipped with robotic arms for loading and unloading parts and a mobile base for transport. It can be modular, where the two entities work together or separately. The existing task assignment approaches for mobile manipulators do not take into account the balancing of robots especially when the robot can change their capacity thanks to their modularity characteristic. In this paper, we demonstrate the efficiency of the bidding mechanism for the assignment of task to robots in order to increase the balancing for the robots use.