Paid for a battery when my gateway was installed. Assumed this meant that, if my power went out, my phone would still work. Today contractors cut through a power line near me, and we lost power for several hours.
The battery clearly was good, all the lights were on. But, I had zero connectivity to the outside world. I had a really high pitched squeal on the phone line - my cordless base station is connected to the gateway's phone connection, and is on its own UPS system. I went down to the gateway, unplugged the cordless base station, plugged in a plain old phone, and had the same high pitched squeal.
My internet also had no connection... I tried plugging into the gateway with ethernet. So what exactly does the battery do for me if it doesn't preserve phone or internet service... just keeps the gateway lights on?
I just did chat with support, and was told that I should go unplug the gateway from the power line if I lose power. Really?
Also, that I probably need to reset the gateway once power's lost to be sure it works. Really?
After reading your post, thought I would share my actual experiences with you, not that I want to contridict anything you were told by a support person since I am just a user of the Comcast systems like you, but hope the following information provides some help to you.
Over the course of having the triple play package for several years now, which includes the home phone service, I have lost power several times. I don't have a battery backup within the rented cable modem/router, but I do have it plugged into an external UPS that is hefty enough to power not only that unit but my cordless phone base unit and a few other electronic devices for several hours. Not quite sure why you were told that you would have to unplug the modem/router unit when power was lost as I have never had to do that but maybe it is because I use an external UPS.
In most power outages, I have continued to have both Internet and home phone service due to the external UPS keeping the power going. In those instances, the cause of the power outage was varied but nothing happened to my cable setup as I still even had cable tv. The one time that power went out and the UPS still kept the modem/router powered but I did not have phone or internet was a time when a tree a few houses down toppled over in a severe storm and took down the electric pole along with the electric line and cable lines that were attached to it. That was a real mess, the roadway looked like a large plate of spagetti made out of all the cables.
Can't say with any certainity about your particular situation but generally the power lines and cable lines are usually pretty close together be they buried or strung from poles overhead. It could be that when the powerline was cut, the cable may have been damaged to the point that while it was still able to keep the modem/router active it was damaged enough to not be able to provide internet or phone service.
While battery backups are a good thing to have and I have had mine keep me going several times, there are times when the damage is severe enough that even though the backup is functioning perfectly the cable functions are not able to provide the service.
Hope this helps.