I can't even count how many times I've tried to use my EMP, then come out of cover and take out an armorless, stealthless team, only to die because my EMP didn't work. Most of the time, it can't be used for some reason, and just fails to activate. Lately, though, I'll use an EMP, then 5-10 seconds later everyone's using armor and stealth again, no problem. It takes about that long to normally recharge an empty stealth or armor bar, and an EMP is much worse than simply running out of energy. Or, rather, it should be much worse.