The Tesla cannon is a shoulder-mounted energy weapon that is powered by electron charge packs. This weapon has a high Strength requirement for its weight and the fact that it's a recoilless energy weapon. The sound of the Tesla cannon firing has also been changed from the one in Broken Steel. The Tesla cannon is considered a unique class of weapon and therefore cannot benefit from the Jury Rigging perk.
The Tesla cannon is rare, especially so if the Courier kills the Van Graffs, thereby eliminating one of the only specialty energy weapon vendors in the game.
The Tesla cannon can fire a total of about 395 times using standard packs, the equivalent of 99 reloads, from full condition before breaking.
After completing the Honest Heartsadd-on, the cannon will respawn in the Brotherhood safehouse footlocker.
The Tesla cannon uses five electron charge packs per shot, and therefore it's only possible to receive one empty electron charge pack from firing the cannon, the same with all energy weapons that use more than one cell per shot.
Due to it previously firing only one shot per reload, it ejects single electron charge packs every shot despite only one being loaded. Also, the electron charge pack will not appear after one shot is fired, and the end of the cannon is retracted, but it still ejects another per shot.
Behind the scenes
The Tesla cannon was originally to be featured in the canceled Fallout: Brotherhood of Steel 2, bearing no resemblance to the weapon in Broken Steel. Described as a "high-powered mass-cannon throwing tessellated plasma forward in an orgy of death and destruction" in the Fallout: Brotherhood of Steel 2 design document, it was to be the so-called "uber-weapon" of player character Maxus. "Uber-weapons" were to be unique weapons for each player character which had to be assembled from 5 parts over the course of the game, or the player could have an NPC assemble one for them. One of the five parts for this weapon was a Tesla coil.