Why does your battery need energy to stop the robot? Just turn off the motors and let friction do the rest....right? What am I missing here?
Friction? That means you need enough energy to overcome that friction just to start the robot. And coasting is not the same as stopping - especially if there is a wall in the way or your bot is rolling down a ramp
But you are right, coasting is more efficient than reversing the motors for a full stop. But try stopping at a red light without using your car breaks - there are many reasons why that is a bad idea.
Why would you include both the potential and the kinetic energy?
A robot goes up a ramp . . . the energy required is different if the robot stops at the top of the ramp, or if it keeps its velocity constant.
Calculating energy consumption is really tricky, and the most accurate way is through experimentation. But before you build your robot, doing the math will get you ball-park values to help you avoid massive redesigns from subjective intuition failures.