How do I order a backup battery for a wifi extender

Concern moved here to the Customer Service help section for greater exposure to Comcast corporate employees (The Digital Care Team) for assistance.

Good afternoon user_3dnud1 I will be happy to assist you further. Do you currently have our Xfinity Pro, service? Or do you have our XFi Complete, currently? Have you already attempted to purchase the battery backup when selecting Shop/Upgrade signed in to your account? Please let me know.