Several PowerBook models from the early- to mid-1990s all shared a common swappable battery, models including PowerBook 140–180. This PowerBook Battery Recharger was designed to charge two swappable PowerBook batteries. At the time, Apple’s laptop designs did not encase the battery inside the laptop, and users were able to swap a low battery for a charged one on the fly.
Until I acquired this PowerBook Battery Recharger, I had never seen one. The color is greenish gray and contrasts slightly from the PowerBook laptops of the time, but matches the tint of an Apple case designed for the same batteries. I acquired the this charger and the case at the same time.