This vintage electrotherapy device (often called a “faradic battery”) was used in the late 1800s–early 1900s to deliver small electrical currents to the body. At the time, electricity was believed to help with everything from muscle pain to fatigue and “nervous conditions.”
Many of these were marketed with pretty bold claims and sold for home use, which is where the reputation for “quack medical” comes in.
This one still has its original instruction sheet inside, complete with notes on adjusting the current and operating the device.