Another gadget I'd like to see is an EMP (electro-magnetic pulse) tool, so all enemy robot in a radius are stunned for a set period of time. The tree would have things like larger radius and longer time stunned
Another cool idea is a teleport ability. It would be at the very end of the energy storage tree, as it would need all 4 energy bars to operate. Another suggestion for the teleport is that it would slow time to a crawl to let you pick the spot you want to teleport to, and not get killed in the process.
Last gadget I can think of is a horizontal slash that sends out of wave of energy to decimate foes. A little idea is here \/
(best artist I know) It would have an upgrade path that would lead to a longer wave, a faster wave, and the wave would go farther.
This post is prone to be edited with more ideas, so be on the look out
(Just wanted to add a little note here, when the game updates with more upgrades, the circle that is present isn't gonna cut it, unless if you have a Batman: Arkham Knight type of upgrade system [has the circle layout but under multiple genres] a layout I would prefer [you don't have to do it, it's your game :D] is this \/)