I know how to toss the battery to the other robot, only I didn't know that in order to proceed maybe was to just throw the battery around to the other robot up until it went to the next level without knowing anything other than that.
The physics engine, I don't know anything about Unity but I think you could maybe change the friction...
Maybe make the tutorial a bit more clear as to what the robots should be doing, and also tell the player that in order to throw the battery use the mouse and give a visual indicator as to where it is going to go (like an arrow pointing to the mouse, straight from the robot that has the battery).
That profile picture I drew it myself, since I'm an artist who barely draws and programs almost a lot. Planning to be balanced so that I also study art/draw at my free time.