This should add some much-needed depth to the tacticality of the
weapon. It's not much: it takes 5 plasma cells to fully charge the
cannon. But it does eliminate the previous effect where the charger
was always preferable over plasma bullets; it's still preferable in
a lot of circumstances, but for smaller ships, it's now typically
better to use plain old plasma ammo. It also limits the amount of
times the charger can be used.