Review SM134: Everyone's Fully Powered! The Road to the Semifinals!!

[JinksChow]

And when was this established in the anime? Zap Cannon has never been depicted to need charging (and doesn't in the games either) or be horribly inaccurate in comparison to an anime attack's usual hit-rate; it operates no different from the other spherical attacks such as Shadow Ball or Aura Sphere. In fact, we've seen several times how Pokemon have launched spherical attacks consecutively (rapid-fire), and even several simultaneously, which invalidates your argument in that respect.

While admittedly a long long time ago, back in AG170 (Ash's rematch against Anabel), Scott remarked that Zap Cannon's accuracy is not that high.