The ATW-CHG3N Networked Two-Bay Smart Charging Dock from Audio-Technica is for the 3000 Series (4th Generation) wireless microphone system. It can be used to charge NiMH batteries inside transmitters. The charging dock features automatic shut off if alkaline or damaged batteries are detected in transmitters. In addition, up to 5 docks can be linked and powered by a single power supply (sold separately) and charging status of all transmitters can be monitored.