Battery Backup for a WiFi Router and Modem: How Long Do You Stay Online?

The power goes out and within ten minutes somebody asks whether the wifi is still working.

It isn't, because the router is dead. And the phones are burning through data and battery while everyone refreshes the outage map.

Good news: this is the cheapest problem in backup power to solve. Bad news: solving it doesn't always work, and it's worth knowing why before you spend.

The numbers are absurdly friendly

A typical home router and cable modem together draw around 20 watts. verify

That's about a quarter of what one old-fashioned light bulb used.

Even the smallest unit here runs your internet for most of a day. A 1,000Wh station runs it for the better part of two days while doing plenty of other work at the same time.

There is genuinely no cheaper win in this whole category.

What your specific setup draws

"20 watts" is the common case. Yours may be higher, and it is worth knowing which.

verify on every figure — check the label on your own power brick, which gives volts and amps. Multiply them for watts.

Two things push people well above the 20W assumption. Mesh systems are the big one: three nodes at 8W each is 24W before the modem, and every node needs its own battery or its own outlet. PoE camera systems are in a different class entirely and belong in the fridge-sized part of your planning, not here.

How long you actually get

These allow roughly 15% for inverter losses. Run the router from a 12V DC port instead of the AC outlet and you claw a good part of that back — see below.

Look at the 250Wh row. A unit that cannot start a fridge, that costs a fraction of what outage-prep articles push at you, runs your internet overnight and well into the next day. If wifi is genuinely your main worry, you are shopping in a much cheaper bracket than you think.

The catch nobody mentions

Your router being powered does not mean your internet works.

Between your house and the internet there's a chain of equipment: a node in your neighborhood, a cabinet down the street, equipment at the ISP's facility. All of it needs power.

Cable and fiber providers do run battery backup at those points. It's finite — commonly a few hours, not a few days. verify

So in a short outage, powering your router genuinely keeps you online. In a two-day regional event, your router hums along happily connected to nothing.

How long your ISP lasts depends on what kind of connection you have, and the differences are large:

The Starlink row is worth a moment. It is the one connection that does not care whether your neighbourhood has power — but at 50–75W it draws three times a normal router, so the runtime tables above roughly divide by three.

Fiber has a specific trap. Many ONTs ship with a small internal battery, or a slot for one, that is often dead or missing after a few years. If you have fiber, check that first — it may be the cheapest fix available to you.

The alternative most people should consider

A phone hotspot.

Cell towers generally have their own backup power and often stay up longer than home internet infrastructure does. A phone plus a decent power bank gets you online for a fraction of the cost and effort.

For a short outage, that's frequently the better answer — especially if all you need is to check on family and look at the outage map.

Keep the home router plan for longer events and for anything that genuinely needs a real connection: remote work, security cameras, a medical device that phones home.

The trick that stretches it further

Most routers and modems run on 12V DC. Your power station stores DC.

Plug into the AC outlet and the station converts DC to AC, then your router's brick converts it straight back to DC. You lose energy at both ends for nothing.

Use the station's 12V DC port instead, with the right barrel connector, and you'll get noticeably more hours out of the same battery. verify

There are two separate savings. You skip the inverter conversion loss, and you stop the inverter idling — an inverter running a 20W load still burns several watts just being switched on, which on a tiny load is a large share of your total draw.

Before you try it, check three things on the router's power brick:

1. Voltage. The label states its output — commonly 12V, sometimes 9V or 5V. It must match the port you plug into. A 12V port into a 9V router is how you destroy a router.
2. Polarity. The little diagram showing which is centre-positive. Most equipment is centre-positive; getting it backwards is usually fatal.
3. Barrel size. Physical fit varies and a loose plug is worse than none.

UPS or power station?

Both work. They're for different problems.

A small UPS is cheaper, switches over in milliseconds so your connection never drops, and it's designed for exactly this. If the router is genuinely the only thing you care about, buy the UPS.

A power station holds far more energy, runs your fridge too, and goes camping. Its switchover is usually fast enough that a router doesn't notice, but check the spec if you care.

Most people should own the power station and use it for everything, rather than buying a device that does one job.

What we would not buy

A big power station just for the router. You'd be spending several hundred dollars on a 20-watt problem. Buy the small one, or the UPS.

A cheap unbranded UPS with a sealed lead-acid battery. They die quietly after two or three years and you find out during the outage. Check the battery is replaceable.

A "modem battery pack" sold as a dedicated product. These exist, they are usually small sealed lead-acid units in a plastic box, and they are frequently poor value against a small LiFePO4 power station that does the same job, lasts far longer, and is useful for other things. If you see one described as a modem or router battery backup, compare its watt-hours against a 250Wh power station before buying — the comparison is often unflattering.

If you work from home

This changes the sizing, because the router stops being the whole problem.

A realistic work-from-home load: router and modem (20W), a laptop charging (45–65W), and a monitor (20–30W). Call it 100W, which is five times the router alone.

1,000Wh is the work-from-home number. It covers a full working day with the internet up, and it is the same size that covers a fridge overnight, which is why it is the size we point most people at anyway.

Two things worth doing in advance: run the laptop off its own battery and only charge it when it gets low, and know your phone hotspot password before you need it. A laptop already has hours of battery — the router does not, which is the entire reason this page exists.

If a desktop rather than a laptop is involved, switchover time starts to matter and the answer changes — we set that out here.

Straight answer

Whatever power station you already bought for the fridge will run your internet almost as an afterthought. Plug it in and forget it.

If you're buying specifically for this, the smallest LiFePO4 unit you can find covers it — and honestly, test how long your ISP stays up first. That number decides whether this is worth solving at all.

Three quick pointers depending on where you landed:

• Router only, short outages. A small UPS, or a 250Wh unit. Our under-$500 picks cover this bracket.
• Working from home. 1,000Wh. The outage guide covers that tier and names who each unit is wrong for.
• You are not sure your ISP even stays up. Do the test in the callout above before spending anything, and read will the internet work during a power outage — for a lot of households the honest answer is a phone hotspot and no purchase at all.