The number in the upper right corner is the total energy value. The number in the bottom right corner is the energy conversion rate.
Go to: Walkr > Menu > Factory > Add a ship to the energy slot
Additional energy storage = original energy storage of the ship in the slot X conversion rate
For example: If you are using SS Doggii, a spaceship with 50,000 units of energy and you then put another ship with a 10,000 unit storage capacity into the energy slot (30% conversion rate), SS Doggii will get 3,000 extra units of energy storage capacity for a total of 53,000 units.
＊Maximum 3 slots available