Various embodiments are described herein for a mobile infusion device that does not use gravity to expel fluid from a bag. The device has a housing with a central chamber connected with an opening to receive a portion of the bag during use. A rotation assembly is coupled to the housing and includes at least one roller located within the central chamber and a spring mechanism operatively coupled to the at least one roller to rotate it to move the bag and apply a force to a portion of the bag to expel fluid therefrom during use. A control mechanism is operatively coupled to the rotation assembly and has a control assembly to control rotation of the rotation assembly and a user interface coupled to the control assembly to allow a user to select a mode of operation for the device. The spring mechanism is recharged in standby mode. Various mechanisms can be used in various embodiments to improve functionality such as a gearing mechanism.