modem on battery backup

I don't see how it could tell the power came from a UPS or the powerline unless your UPS doesn't have a decent waveform that it can somehow detect. To be honest, the wall-warts these things use shouldn't notice the difference.

I do believe the "party line" is (somehow) correct as I have had the modem connected to a UPS for YEARS with 2 batteries in the modem and the ride-through should have been close to 8 hours but it only lasted 1 hour. Furthermore, after power restored the Comcast callcenter said my battery was showing 100%.

I have heard before (but remember little) that one UPS plugged into another UPS is a bad idea because of the nature of the waveform created by #1 is analyzed by #2.

I suppose the solution is simply to remove (both) batteries from the modem and rely solely upon the UPS!

After "years" of use I would suspect that the battery is not working at its full potential any longer. That might explain why it lasted 1 hour instead of 8.

Now that it has been on "line" for a couple of days, maybe I should just pull the plug and see how long it lasts. Wait, that would disconnect my internet!

People have been known to survive short periods of time without Internet, so it's not as risky as it seems.

What model modem (or actually, eMTA) is it? Does it actually have 2 batteries? Do both work? I thought most just had one supply that ran both the phone and internet. It's a bit odd that it may have 2 separate supplies.

In the eMTAs I've had from Comcast, the internal battery operates phone but not Internet. They have room for two batteries, typically, but Comcast supplies one. I've never had two models that share the same battery.

UPS would be the only solution to maintain Internet access.

But it turns

power source

Surely you jest!

Yes, but the installer gave me two because I asked.

'fraid so!