This is the description for the Engineer's Charge Mechanic
The Charge bar, located just above the bottom center of the screen, forms a progress bar showing how much progress has been reached. Assuming that it is not left inactive, the Charge bar will retain it's charge, increasing until it reaches 100% with every time you hit something. As above noted, your skills
will often consume some Charge, but every time Charge is used, it can be regained by damaging more enemies. No physical attack benefit is given when the Charge bar has reached maximum, unless you have a skill
that changes that.
Every class in Torchlight II
has 21 actives and 9 passives adding up to 30 skills total spread across 3 Panes evenly.
The Engineer's panes focuses around the hard hitting in the Blitz Pane, Engineering in the Construction Pane, and the defender in the Aegis Pane.