@arma473 You do realize they are not only for Overcharge, right?
If you want to see in what situation I found them useful, try playing Operation Golden Crystals solo: Attacks come from all directions, bombers bomb everything, I build T2 factory and spam Sparkies: I get overcharge, they assist with building, build defenses, and shoot enemy units and don't die fast (1000 HP). Of course, after some time, I build Energy Storages.
Here is a replay: https://replay.faforever.com/17891487