Previously i used an energy reservoir system for hijacking units. Every unit needed energy to hijack with some requiring more energy than others. 

Energy recharges naturally and is also used for shields so when the player took a hit that the shield blocked, energy would be lost. In actual gameplay the energy system was too complicated for players to understand with the default behavior becoming 'look at the thing i want to hijack until it turned green'

So i spent a day rebuilding it. Now all the player has to do is look at the unit they want to hijack and hold down the action button until the bar fills up. This mechanic only has one rule which is don't break line of sight for too long otherwise the counter resets. 

Now units have a unique hacking timer so bigger and more powerful characters and vehicles like tanks and helicopters will take longer to hijack compared to foot soldiers and drones.