I'm not sure how its done but in multiple games I have joined, all the enemy jackboots have been fully overcharged making them harder to take down, but still possible. Just thought I would let you guys know.
I have seen this too, I was going to post it in my glitches feed back thread, but not sure if this is something that is supposed to be possible. A group tried it with three supports on juice and that didn't work though so we're thinking it is a glitch.
Actually, I think that it doesn't show overcharge on friendly Jackbots. I think I't only shows it on enemy Jackbots. If your juice bar is going up then your healing or overcharging it.
The reason I made an account here was to say that I've started coming across overcharged Jackbots. I guess I'm not the only one.