Battles are shown as a pre calculated replay. The battle can be paused and resumed with the button in the top right corner. The central button at the top changes whether or not the team colours are used to display the ships. Darker colors indicate higher damage. The green button on the top right allows a screenshot to be captured. The slider at the bottom of the screen can be used to adjust playback position.
The icons at the top are health icons. They transition from green through yellow, orange, red to 'gone' when a ship is damaged. If the fleet is destroyed it will have no ships. The battle is over either when the time runs out (about 2 minutes) or when a fleet is destroyed. I am yet to see two fleets completely wipe each other out!
Pressing the back button on your device will take you back to the menus.