Mobile platform: Linear actuatorAn electro-mechanical linear actuator can be a good choice for light weight actuator which can be mounted on mobile platform.
Battery powered: LinearAn electro-mechanical linear actuator is good choice over servo motors, as linear actuators draw power only when it is moving, and it does not need power to hold its position.
5-6 DoF: It might be difficult to achieve this using electro-mechanical linear actuatorsactuator, as they are mechanical complicated and have limited range of motion
You can try linear actuators from www.firgelli.com. They have miniature linear actuators as well, which are good for small scale application.
Mechanical design concept for arm using linear actuator: Most of earth moving equipment have hydraulic linear actuator. Some of the joints for linear actuator can be implemented in this line.