You can use any modem that supports DOCSIS 3.0 or DOCSIS 3.1 and it should ideally be compatible with Charter Spectrum internet connection. However, it is best advised to go for a modem that has already been approved by the ISP so that you know that you are getting the right kind of internet experience. Getting a mismatch there would mean you are paying for a better connection but getting only an average performance in return.