Heated humidifier for the Respironics M series of CPAP machines. The M series heated humidifier fits comfortably with the CPAP machine to form one tightly integrated machine. Respironics has added a DC compatibility feature for CPAP users who would like to connect a DC battery source to their CPAP. The M Series DC Compatible Heated Humidifier works with any model within the M Series product line. (DS100, Plus, Pro, Auto, or BiPAP) Use the DC input on the back of the humidifier to supply battery backup to both your CPAP and Humidifier. Batteries like the CPAP.com Battery Pack will provide up to 4 hours of battery backup for your system.