Remote Electrical Charge

The Remote Electrical Charge gun (nicknamed    the REC Gun or simply REC) is a weapon that can shock people with electricity and power up generators and industrial electromagnets.

Summary
This weapon could also be used in combat during a Freeflow Combo and was used by Batman. This gadget was obtained in the Steel Mill while in Arkham City and was used prominently in the Industrial District. In Arkham Knight, it could be obtained very early in the storyline, as Batman could break the display case the gadget was held in as early during his first visit to the GCPD Building, however the player wasn't instructed to do so until a certain point in the game.

Combat
The Remote Electrical Charge gun was capable of stunning thugs and disoriented for a brief moment. However, the REC was more useful on armored enemies as they were knocked down when the REC connected with them, or on enemies with stun batons as they swung their batons and stunned other thugs around them. It also could incapacitate Titans, make Lieutenants brandish their weapons around causing Collateral Damage. If fighting goons and Titans at the same time, use the Remote Electrical Charge Gun to stall a Titan so you could have a little extra time to fight off the thugs. During Predator Challenges, Remote Electrical Charge Gun can be used to distract armed enemies. If fired at enemies, the electric shock was non-lethal.

In both City and Knight, the Freeflow gadget upgrade powers it so that when used, it chains the electricity to multiple targets nearby.

Batman: Arkham City
The Remote Electrical Charge was first gained when you rescued Dr. Stacey Baker and after Joker's Henchmen sealed the door of the Smelting Chamber. Quickfire Remote Electrical Charge was LT + B (XBox 360), L1 + O (PlayStation 3) and 4 + 4 (PC).

Batman: Arkham Knight
Shortly after the events of Arkham City, Batman turned in all of his evidence of Arkham City, including the REC which was locked up in the Evidence Room with the other supervillain gear. Aaron Cash notes it is nice to have some of Batman's gear in the evidence room (just in case something bad happened) and humorously hopes that Batman doesn't ask for it back.

Sometime during the event, Batman went into the Evidence Room and reclaimed the weapon he made by smashing the case that it was in.

After the event, Nightwing started using the gadget, presumably inheriting it from Batman after The Knightfall Protocol.

Trivia

 * At least in Knight (City unknown), the projectiles that the gun shoots are not simply balls of electricity, but a small orb surrounded by electricity. This can be seen if the player zooms into the projectile in photo mode. This explains why the gadget can break windows.


 * If Batman used the REC on Solomon Grundy, he would temporarily regain health, and turn blue.
 * It was unknown how Batman had constructed the REC, as he simply pulled out a device out of a random, nearby cabinet, connected it to a grapple gun looking device, and somehow made it a fully functional taser shotgun.
 * Interestingly it is one of the few gadgets (along with the Ultra Batclaw and presumably the Line Launcher), known to have been constructed by Batman himself, and not Lucius Fox.
 * You could shoot the REC at the TYGER Helicopter which made them fire their guns at you. Even though you used the Disruptor on them, it jammed their gun for a temporary amount of time. This also works with throwing a Batarang at the TYGER Helicopter.
 * Batman drew the REC on a sticky note and stuck it on the top left side of the cabinet next to his work bench in Batman: Arkham Origins. Though it was unknown how Batman would draw it if he created it in Arkham City. It was likely he drew it as a concept for a gadget back then and even made one some time later after Origins. This would explain how he knew how to construct a crude version in Arkham City.
 * In Arkham Knight, Batman can obtain the REC from the Evidence Room at any point after bring Poison Ivy to the GCPD Lockup, by simply breaking the glass of its display case. Humorously, after retrieving it and leaving the evidence room, the female GCPD officer guarding the door will say "I ain't stoppin' em." and her male partner responds, saying "Me, neither.. However their reaction is understandable given the severity of the crisis Gotham was in during the events of Arkham Knight and given their respect for Batman. If this is done after the Ace Chemicals incident, a hallucination of the Joker will laugh: "I know this is the evidence room, but seriously." right after Batman breaks the display case with the device.
 * If the player looks closely in Arkham Knight, they can see electricity crackling at the end of the barrel. This does not occur in Arkham City.