According to the wiki, there is not only a blueprint for them, but also unique components to craft it and such, all with textures, working formulas and basically ready to be put into the game.
But the only example of shield recharging I ever seen in the game are the plasma sentries in Arke power plant.
I wonder if there are any plans to implement them (perhaps in an expansion/DLC/sequel/whatever?) or is just an abandoned idea that didn't make it into the game? I predict it's the latter, but they would be great to have, especially in those rare fights where enemies use EMP grenades.
