Normally Comcast should have a list of updated compatible modems. I would say take down the model number of this modem and call them to verify that its compatible with their services. Based off that answer make ur purchase. Now to answer your question about one having a battery backup.. the modem your looking at comes from the same line that mine does and there isn't a battery that goes with it. In the box they give you the ethernet cable to connect to your computer and also the power cable to physically plug into the electrical outlet. With connecting your phone, if you have a smartphone like an android or iPhone the wifi could work on the device from the modem. One thing I was advised of also before I made a purchase of a similar modem was to make sure the speed of your internet plan is compatible with modem otherwise that can also cause a lot of issues.