"DPCSIS 3.0" is not a valid model number. Please see https://www.xfinity.com/support/articles/broadband-gateways-userguides for model numbers of Comcast gateway devices.
Just a note that the battery on Comcast gateways only powers the phone service. It will not run the full Internet connection. You may be better off getting a stand-alone UPS and plug the gateway into that, as it will power the full gateway.
My modem is XB3 Model DPCSIS 3.0
I need a battery number to fit this modem.
Yep...... 😞 That would be the preferrable way to go ! You can even plug your other equipment in to it.
Or buy a refurb modem that includes the battery at that price.
I have a backup battery and a UPS, but the connection and phone still goes out when the power goes out, as the local repeater on the pole does not have a backup