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Eaton UPS for router

Updated: October 2026

The landline is digital voice, the fibre light is on a small white box in the hall, and the router is in another room on a different plug. An Eaton UPS for router backup only keeps the phone and the broadband up if the Openreach ONT and the router are both on battery power. Backing up the router alone leaves the fibre dead. The seven Eatons, with prices from the amazon.co.uk snapshot of 19 October 2026, are on the [Eaton UPS comparison](/hub/electrical-equipment/eaton-ups). We did not time your ONT. A qualifying purchase can earn a commission at no extra cost to you.

The landline is digital voice, the fibre light is on a small white box in the hall, and the router is in another room on a different plug.

Our top picks

Eaton Eaton 3S700B 700 VA

Best overall

Eaton Eaton 3S700B 700 VA
9.2/10about £124.06
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Eaton Eaton 3P700I 700 VA

Rank 2

Eaton Eaton 3P700I 700 VA
9.2/10about £118.61
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Eaton Eaton 3S Mini 36 W

Rank 3

Eaton Eaton 3S Mini 36 W
7.4/10about £53.99
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On this page
  1. 1.What actually has to stay on
  2. 2.The 3S Mini’s one output
  3. 3.Tips that do not fit
  4. 4.When to use a tower instead

What actually has to stay on

Digital voice dies when the ONT dies, even if the router still has power, because the router has nothing to route. In a full-fibre house the ONT is often on the wall by the front door and the router is in the study. They are two plugs. If you only move the router onto a UPS in the study, the next cut still takes the phone. Eaton’s Mini examples sit around 9 W to 15 W. A lead-acid PC UPS can run a 10 W ONT for a long time and still be the wrong tool if it is under a desk two rooms away. The watt sum for a PC is on how to size an Eaton UPS.

The 3S Mini’s one output

The Eaton 3S Mini, model 3SM36B, ASIN B092TG9M7C, is the DC candidate in this set. It is £53.99, rated 36 W, with selectable 9, 12, 15, and 19 V, and one output. It cannot feed an ONT and a separate router at the same time unless you add a splitter the listing does not provide. The star line is 3.6 from 190 reviews. Batteries failing around two years come up more than once. Set the voltage to the label on the device before you connect anything. A wrong DC voltage can destroy the router. The listing’s runtime fields disagree, at 5 hours and at 150 minutes. Eaton’s Mini datasheet gives about 80 minutes at 9 W and about 40 minutes at 15 W. The amazon plug attribute says no plug. Check the lead that arrives.
Eaton Eaton 3S700B 700 VA

Testsieger

Eaton Eaton 3S700B 700 VA
9.2/10about £124.06
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Tips that do not fit

Amazon bullets for this ASIN list tips of 3.5×1.5 mm, 4.75×1.7 mm, 5.5×2.1 mm, and 5.5×2.5 mm. Eaton’s low datasheet lists 3.5×1.35 mm where the listing says 3.5×1.5 mm. Those lists do not match. UK reviews say the box lacks a tip for some Asus routers, often the 4.0×1.35 mm plug, and that the BT Smart Hub 2 connector is not in the carton. Forcing a 3.5 mm plug into a 4.0 mm socket is how you get an intermittent cutover that looks like a bad battery. If none of the tips seat, the Mini is the wrong ASIN for that device. Leads and sockets are on Eaton UPS UK sockets.

When to use a tower instead

Use an AC tower when the ONT and the router already sit on BS 1363 plugs in the same place, and you can put both in battery-backed sockets. The 3S700B is the only title in this set that describes BS outlets, four with battery backup and four surge-only, at £124.06. A surge-only socket still kills the router in the cut. For this small load you are buying minutes and sockets, not brownout correction. An IEC tower is the awkward shape unless you already have C14 leads, which home ISP kit almost never does. If the two boxes are in different rooms, two small supplies beat one large tower in the wrong room. A desktop pick is on best Eaton UPS.

Common questions

Which voltage do you set?
Set the switch to the voltage printed on the device or on its original adapter, before you connect the barrel. The Mini’s bullets offer 9, 12, 15, and 19 V. A 19 V setting into a 12 V ONT is not a harmless mismatch. Wrong DC voltage can destroy the router or the ONT.
Why do Asus and BT Smart Hub 2 reviews mention missing tips?
Because the tips in the carton do not cover every UK hub. Reviews of this ASIN say some Asus routers need a 4.0×1.35 mm plug that is not included, and that the BT Smart Hub 2 connector is absent. Compare the plug you unplugged with the tips in the box. If none seat fully, this Mini is the wrong fit.
How long might a 9 W or 15 W gateway last, according to Eaton?
Eaton’s Mini datasheet gives about 80 minutes at 9 W and about 40 minutes at 15 W. Those are examples for those loads, not a test of your Openreach ONT. The amazon listing instead prints both 5 hours and 150 minutes, which cannot both be the specification. UK reviews describe packs failing around two years.
Is a lead-acid PC UPS a bad tool for a 10 W ONT?
It is a clumsy tool when the ONT is alone in the hall and the UPS is built for a PC under a desk. A 10 W load sits far under 420 W. The failure is distance, the plug, and the surge-only sockets. If the ONT is a barrel in the hall, the Mini is the closer match, once the tip and the voltage agree.
When is a second small UPS the honest answer?
When the ONT and the router are in different rooms, or when the Mini’s single barrel fits only one of them. One tower in the study does not resurrect a hallway ONT. One Mini does not feed two barrels. A second 36 W unit, or one AC UPS placed where both mains plugs already are, matches how full-fibre kit is actually installed.

Related pages

Eaton UPS buying guide

Eaton UPS

Best Eaton UPS: top pick for UK plugs or IEC leads

How to size an Eaton UPS before you trust the minutes

Eaton UPS UK sockets: BS 1363 outlets or C13 leads

Sources

Public sources from the research digest, last checked on 19 October 2026. Shelf prices and star lines are the amazon.co.uk figures in the display file.

  1. Eaton 5E Gen2 datasheet (en-GB) (retrieved 19 October 2026)
  2. Eaton UK UPS buying guide (retrieved 19 October 2026)
  3. Eaton 3S700B product page (retrieved 19 October 2026)
  4. Eaton 5S550IBS product page (retrieved 19 October 2026)
  5. Eaton 3S Mini catalogue page (retrieved 19 October 2026)
  6. BSI: BS EN IEC 62040-3:2021 (retrieved 19 October 2026)
  7. Electrical Equipment (Safety) Regulations 2016, regulation 35 (retrieved 19 October 2026)
  8. GOV.UK: Electrical Equipment Safety Regulations 2016 (retrieved 19 October 2026)