Battery backup for internet service?

I used to like to have a separate, actual phone line in case of natural disaster that knocked out or overwhelmed the cell towers. But I just moved and discovered that new phone service (at least where I live) can only be installed running through the internet router, not the old dedicated phone lines.

Okay, fine, I can still make calls or use text/email through my internet service…as long as the router is working, meaning the power’s still on.

So, in case the power goes out, I was thinking I’d buy a battery backup for the router and modem. However, if power goes out, will that kill my internet connection entirely? In other words, will I have a working router that connects to a “dead” coax cable?

I have Spectrum and live in SoCal if that makes a difference.

Ask your provider, some of those units already have a battery backup on the telephone side of the system

They will only sell me a battery backup if I pay for their phone service, which I don’t want. I can buy my own battery backup cheaper.

The fact that they offer a battery backup suggests that the internet will still work in case of a power outage, but I don’t trust them to tell the truth. I’m hoping someone with knowledge of the way this works can weigh in.

As I understand it, the telephone UPS is required by the FCC-all POTS connections have to work when the power is out. It used to be a safety issue. I suspect that if there is a major power outage effecting the phone lines, POTS will be all that the phone company supports. Whether you have a UPS won’t matter if the phone company isn’t passing packets to the backbone. Of course if it is a local outage, the phone company switches will continue to work as normal and I imagine your internet will continue.

Remember, the level of service that the phone company provides is set by the FCC and the state and applies first and foremost to POTS. Internet is still considered a nice to have feature and the phone company is held to a lower level of required service for such add-ons.

The only way to be sure is to ask your state regulator. They can tell you what the phone company is planning to provide in each scenario.

It’s been my experience with cable phone and Internet service that as long as the lines aren’t severed, you will still have service if you provide power to your modem, router, and computer or phone.

I have 4 UPSes in my house, and when the power goes down, typically from a tree falling on the power line, a consumer-grade UPS will keep the router & modem running for 3-4 hours as long as a computer isn’t connected too (a computer draws much more current).

The phone modem supplied by the cable company has a socket for a battery backup independent of (actually in serial with) the external UPS. It has a capacity for a 10 hour battery if you are only using it in standby mode. Again, this is a very low current draw.

I don’t know how the cable companies power their nodes which feed multiple houses or businesses, but these rarely go down in my neighborhood. They must have some kind of power, or the signal would stop.

I use Cox, and have a backup battery in my phone modem. If the power goes out (or if the modem gets unplugged, which is how I found out) the phone will work on battery, but not the internet connection.

This is also my experience. With the cable modem, router, and wireless AP (whether that’s one, two, or three devices) all connected to a UPS I’ve continued to have internet service even when the power is out. This has held true for outages of only a few houses and widespread outages in the whole city.

Thanks for the replies.

I’m mainly concerned about the ability to use my cell phone to make calls or just send emails/texts in an emergency situation, so powering the computers isn’t an issue–though I guess I’d use the laptops until the battery died to save cell battery, and we have portable phone rechargers that are kept full.

I’m not worried so much about the “tree on the power lines” scenario as an earthquake. Now, it’s possible an earthquake would disrupt cabled internet service too, but with a battery backup at least I have two potential ways to communicate (cell phone, internet) instead of one.

Partly true in my experience. When the power goes out I can start up the generator and run a lead into the house. I have cable, Internet, and phone. Except…

Except two or three years ago we had a power outage that lasted three days. We lost cable/Internet/phone after four hours. There’s a cable box at the top of the power pole in front of our house. Apparently it contains a 12 v battery that provides power to the unit in case of a power outage. But it only lasts about three or four hours. The second day the cable company came out and put a gasoline-powered generator on top of the box. It was only then that we got our services back… but we still had to run our own generator to power the box/modem/phone/TV, etc. to make use of those services.

My phone switch info is 20 years out of date, but #5ESS switches and the 3B-20 computers which furnished their computer power actually ran on batteries which were continually recharged, like laptops.
When I was involved in chip design for transmission systems, I found that there was a requirement that the system no overheat even if the fans went out for a certain amount of time.
For POTS I don’t know if the SLC systems (which multiplex subscriber lines to reduce the number of lines the central office receives) would stay up, though I assume they would have batteries also. I don’t recall seeing the architecture of a full SLC system.

Interesting that you mentioned a gas generator supplied by a utility.

Some years ago we had reoccurring Internet outages, a few hours at a time, and seemingly not weather-related. Naturally, I’m the first to notify Charter when an outage happens, and they were getting near-daily calls from me.

But why so frequently? The mystery was solved when a friend spotted a small gas generator parked next to a utility pole, running, with output lines going up the pole. Calling the local supervisor on his secret, private line, we got him to admit that the generator was powering their cable system’s node box. They felt that the power supplied by the power company was irregular, and they wanted to test the theory that that was the problem by supplying their own power source.

But when the generator ran out of gas, we ran out of Internet. Hi-tek, you bet.

I have a smallish consumer type UPS dedicated to the cable modem and router. As others have reported, I get hours of continued service for both landline and Internet. I haven’t seen an outage the backup power couldn’t outlast.

There is a big slab of “it depends”.

This week my POTS phone line gets cut over to shiny new FTTC (fibre to the curb) National Broadband Network in Australia. The physical copper connection will only go from in my house as far as the pit outside my house, with the link back over brand new fibre. I get no choice in this, even if I didn’t want FTTC, the trunk copper will eventually physically go. The up side for me is that the new FTTC termination devices are in the pit and are powered from the premises - so I can add a UPC and it will actually power things and my link will stay up. I get a (free) VoIP phone line, and in principle, it will still work if my UPS can power things.

For other NBN customers here in Oz it gets harder. Those with FTTP (Fibre to the premises) they can also use a UPS to power the termination device, and keep the phone alive, but is a bit messier. Those with FTTN (fibre to the node) where the fibre only runs to a box somewhere withing about 100m of their house are SOL. That box is powered from the local power lines, and has no UPS. A local loss of power, and there is no internet. Same for people with internet via cable. (HFC).

All the above is for Oz, and the miracle that is the NBN, and its multi-technology roll out. But it gives a flavour of the range of issues. Bottom line is whether the next step from your house will survive a local power outage. You will need to ask.

I have almost the exact same set of issues. I live in a bushfire prone area (I was on TV last year when a fire ran up the hill, half way up my property, and I got to watch planes water bomb my property whilst standing by my back door.) Cell reception is dreadful (and won’t get better after the local NIMBYs nixed an upgrade to the nearby cell tower.) So I was very loath to give up my POTS line. But I have no choice - it is going away. I already have the UPS ready for when my service is cut over. OTOH, 100Mb/s down, 40Mb/s up, will be pretty nice.


Unless you’re running a private “nano site” to boost cell signal, your home’s internet connection has nothing to do with your cellular phone service.

For Voyager’s old-school flashbacks to Ma Bell’s systems, pretty much everything from the 3B20s and 5ESS switch down to the coffee pot ran on battery power, so there was absolutely no switchover delay in a power failure. Today, we’d call that an “on-line” UPS, as opposed to the cheap consumer-grade ones that are “standby” and take a brief moment to take over when the power fails.

I have VoIP and a battery backup. With one exception, at least 90% of the time when the power goes out the cable connection goes, too.

The exception: The transformer breaker in front of our house pops and has to be reset. This happens surprisingly often and mostly without any apparent reason.

So, it’s good to have the backup then.

I think the copper-line POTS or PSTN network is being decommissioned. I’ve seem some discussion of a complete phaseout by 2025:

Formerly a copper line was required for critical applications like commercial fire alarms. The reasoning was those were self-powered from huge banks of wet-cell batteries in the central office, and that power ran over copper lines all the way to your house phone. Provided the line wasn’t physically cut, the phone would continue to work for a long time, even if all other utility power was out.,c_limit/Payne003.jpg

However in many areas, digital telecom is being allowed to replace those, even in fire commercial auto-dialing fire alarms. The reasoning is the old PSTN network is expensive to maintain and has limited capability. The telecoms don’t want to maintain two separate networks. In theory the old PSTN copper network and related switching infrastructure is more reliable in a power outage situation, but that network itself is degrading as it ages. That includes an aging copper cable plant, and aging switching infrastructure. Despite the self-powered feature, at some point it becomes less reliable than digital voice telephony.

I don’t know the current telecom installation standards for new residential and commercial developments, but they may not even pull copper telecom lines anymore. So the PSTN network physical infrastructure may already not exist in many places.

Digital phone lines (not just VOIP) require on-premesis power, and are subject to software/hardware malfunction of the cable modem. Those lines often run to a neighborhood VRAD or other concentrator box which also must remain powered. Each node in the digital telecom chain may have limited local battery backup but once those batteries run down or if hardware, software, or network failure happens, the service is disrupted.

But there is no real choice – the old copper PSTN network cannot be maintained forever. The digital telecom system is improving in reliability, although it still requires multiple powered nodes. From a residential consumer standpoint I think your only choice is have a UPS for your cable modem and any related on-premesis telephony hardware, also use your cell phone for backup. In some cases you may need to input E911 data to your cell phone to ensure it forwards this to 911 dispatchers if using WiFi calling:

In the event digital wireline telephony, packet-swiched internet, and cellular systems are all locally down, in theory you can send text messages using a MESH network device like GoTenna or Sonnet. However this depends on how many people are in your vicinity are using those :


There are many ways to make calls with a smartphone using internet but not cellular service.