Modem Battery Packs: Are the Dedicated Ones Worth It?

Compare on watt-hours, nothing else

Every one of these products describes itself in a different unit — mAh, "hours of backup", "keeps you online during outages". Convert everything to watt-hours and the comparison becomes obvious.

If a listing gives mAh, multiply by the voltage and divide by 1,000:

20,000mAh at 12V  = 240Wh
20,000mAh at 3.7V = 74Wh   <- the same "20,000mAh", a third of the energy

That gap is why mAh is the unit these products prefer to advertise. A number in mAh with no voltage beside it tells you nothing at all. Our watt-hours to amp-hours guide covers the arithmetic properly.

What each size actually buys you

A router and modem together draw around 20W. verify

Allowing roughly 15% for conversion losses.

The 40Wh row is where a lot of dedicated packs sit. Two hours covers a brief flicker and nothing else — and brief flickers are exactly the case where you also have the option of doing nothing.

Where the dedicated pack genuinely wins

Two real cases, and they are worth taking seriously rather than dismissing.

You need zero-gap switchover. A dedicated pack sits inline and takes over instantly, so the connection never drops. If you are on a video call and the lights flicker, that matters. Many power stations do this too via UPS pass-through, but not all of them — we cover the switchover spec here.

It has to disappear. A small pack velcroed behind the modem in a cabinet is invisible. A 250Wh power station is a box on a shelf. In a rented flat, or where the modem lives in a hallway cupboard, that is a genuine argument.

A third, weaker case: DC output that matches your router. Some packs provide 12V directly, skipping the inverter entirely. Good — but a power station with a 12V port does the same thing.

Where they lose

Chemistry. Many dedicated packs and cheap UPS units use sealed lead-acid, which typically needs replacing every three to five years verify and dies quietly. You discover it during the outage it was bought for. LiFePO4 rated for thousands of cycles does not do this.

Single purpose. It runs a modem. That is all it will ever do. The same money in a small power station runs the modem, charges phones, powers a lamp, and goes camping.

Value per watt-hour. This is the big one. Dedicated packs are frequently priced against the convenience rather than the energy.

The question to answer before buying anything

How long does your internet actually stay up when the power goes out?

Powering your modem does nothing if the neighbourhood node is dark. Cable nodes commonly run a few hours on their own batteries; fiber cabinets often last longer; 5G towers usually have generators. verify

So the honest sequence is:

1. Next outage, note how long your connection survives with the modem on any battery — even a laptop tethering.
2. If it dies in 90 minutes, no battery you buy fixes that. A phone hotspot is your answer.
3. If it stays up for hours, now you know what capacity to buy.

Will the internet work during a power outage walks the whole chain, and it is the page to read before spending anything on this.

Fiber owners: check this first

If you have fiber, your ONT very likely has a battery slot, and there is a good chance it is empty or holds a battery that died years ago.

A replacement ONT battery is often the cheapest possible fix for this entire problem, and it is purpose-built for the equipment. Check the ONT before you shop for anything else.

You still need to power the router separately — the ONT battery typically only covers the ONT.

What we would actually buy

For most people: a 250Wh LiFePO4 power station. Around ten hours of internet, plus phone charging and a lamp, plus a battery that will still be good in eight years. Our under-$500 picks cover this bracket honestly, including where the money stops working.

If zero-gap switchover matters: a small UPS, or a power station with a published switchover time. Not a cheap unbranded pack.

If you work from home: skip all of this and buy 1,000Wh. The router is 20W, but the laptop and monitor take you to about 100W, and a full working day needs the bigger unit. The full arithmetic is here.

The short version

Convert everything to watt-hours and compare. Most dedicated modem battery packs lose badly to a small power station on that one number.

Buy the dedicated box only if you need instant switchover or it genuinely has to be invisible. Otherwise buy 250Wh of LiFePO4 and use it for everything.

And test how long your ISP survives before spending anything — for a lot of households, that test makes the whole purchase unnecessary.