Eaton UPS buying guide
Updated: October 2026
You have already settled on Eaton, and amazon.co.uk is still offering a 36 W battery, a 420 W tower, and a 1,200 W unit as if they were the same spare. This Eaton UPS buying guide uses the seven listings in our [Eaton UPS comparison](/hub/electrical-equipment/eaton-ups) to separate those jobs before you look at the star line. We used the amazon.co.uk snapshot of 19 October 2026 and Eaton’s UK pages. We did not time a power cut in a lab. A qualifying purchase can earn a commission at no extra cost to you.
You have already settled on Eaton, and amazon.co.uk is still offering a 36 W battery, a 420 W tower, and a 1,200 W unit as if they were the same spare.
You have already settled on Eaton, and amazon.co.uk is still offering a 36 W battery, a 420 W tower, and a 1,200 W unit as if they were the same spare. This Eaton UPS buying guide uses the seven listings in our Eaton UPS comparison to separate those jobs before you look at the star line. We used the amazon.co.uk snapshot of 19 October 2026 and Eaton’s UK pages. We did not time a power cut in a lab. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Output | Rated power | AVR | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Eaton Eaton 5E900UI 900 VA | Line-interactive AC | 900 VA / 480 W | Not stated on listing | 9.2 | about £118.57 | View offer |
 Eaton Eaton 3S700B 700 VA | Offline AC | 700 VA / 420 W | Not claimed | 9.2 | about £124.06 | View offer | |
 Eaton Eaton 3S Mini 36 W | DC barrels | 36 W | Not an AC UPS | 7.4 | about £53.99 | View offer |
On this page
Three Eaton jobs in this set
Start with what has to stay alive, because these seven rows are three kinds of product that share a brand. The Eaton 3S Mini is £53.99 and rated 36 W of DC. It feeds one barrel-plug device at 9, 12, 15, or 19 V. It will not run a desktop.
The offline AC towers are the 3S700B at £124.06, rated 700 VA and 420 W, with BS outlets in the title. Offline, on these listings, means the battery takes over in a cut. Automatic voltage regulation is not in their bullets.
The line-interactive rows are the 5S550IBS at £111.43, rated 330 W, with AVR claimed on the listing, and the 5E900UI at £118.57, rated 480 W. Eaton’s en-GB 5E datasheet describes a 140–300 V window that the 5E can correct without the battery. None of the seven is online double-conversion.
Watts, not the VA headline
The number in the model name is usually VA, and Eaton’s UK buying guide tells you to add the watts printed on the devices instead. On the 3S700B, 700 VA is 420 W. Eaton states that split for the 700 VA 3S models, a power factor of 0.6. A 500 W PC does not fit inside 420 W, even though 500 is less than 700. The amazon title on the 5E900UI says 900 VA, and the en-GB datasheet pairs that catalog number with 480 W.
Eaton’s buying guide then asks for about 20% more VA than the load, and it asks you to stay under about 80% of the UPS capacity. The worked sum for a monitor and a NAS is on how to size an Eaton UPS.
Battery outlets and the plug
A socket on the back is not automatically a socket that lives through a blackout. On the 3S700B listing that is four BS outlets with battery and surge, and four BS outlets that are surge-only. Put the router in a surge-only socket and the broadband dies with the street, while the PC on the other bank keeps running. The 5S550IBS listing is the same pattern in IEC: three C13 outlets with battery, one surge-only. The 5E listings in this set do not state a battery-versus-surge split. In this set only the 3S700B title describes BS outlets. The lead arguments are on Eaton UPS UK sockets.
What not to treat as a spec
A few fields in the listings will waste an evening if you read them as engineering. The 5E900UI output attribute says 900 V AC, and the 5E2200UI attribute says 2,200 V AC. Both have copied the VA figure. Mains output on these towers is in the 230 V class, which is what the input fields say. Do not apply BS EN IEC 62040-3, the AC performance method, to the 3S Mini. BSI’s scope for that part leaves DC UPS outside it. The Mini can still be the right box for one router. It is not a small 5E.
One UPS will not cover two rooms
One UPS will not cover a hall ONT and a study PC unless both loads are on battery-backed outlets of a unit that can feed them. The Mini has a single DC output. We are not naming a single winner on this page. If the street voltage sags, the offline rows are the ones that do not claim a cure. If every plug in the house is BS 1363, the IEC towers are the ones that need leads you may not own yet.
Common questions
Is 700 VA the same as 700 watts on an Eaton 3S?
No. On the 3S700B, Eaton rates the tower at 700 VA and 420 W, which is a power factor of 0.6. A device label in watts has to fit under 420 W, not under 700. The 5E900UI is the same kind of split: 900 VA on the amazon title and 480 W on the en-GB datasheet.
When is line-interactive worth it over offline?
Line-interactive is the useful step when your supply sags or spikes and you want that corrected without emptying the battery. In this set the 5S listing claims automatic voltage regulation, and the 5E Gen2 datasheet describes a 140–300 V window without the battery. The 3S and 3P rows are offline and do not claim AVR. The 5E and 5S units here use IEC outlets.
Why are some outlets dead in a blackout?
They are surge-only. On the 3S700B, four of the eight BS outlets have battery backup and four do not. The 5S550IBS listing marks one of four IEC outlets as surge-only. A router or a NAS left in the surge row drops with the mains while the PC on a battery socket stays up.
Does UKCA on the 5E datasheet mean the plug is BS 1363?
No. UKCA on the 5E Gen2 datasheet is a certification line for that family. The 5E900UI in this comparison is the IEC version, with C13 outlets, not the BS part 5E900UB. A UKCA mark does not rewrite the connector, and it is absent from the 3S Mini datasheet used here.
What should you ignore in the 5E2200UI listing?
Ignore an output of 2,200 V, a material of cotton, and a colour of mahogany. The output attribute has copied the VA rating. Treat the unit as a 2,200 VA, 1,200 W line-interactive tower with six IEC C13 outlets, a 52-minute runtime field, and a plug attribute that says no plug. The price on 19 October 2026 was £376.32.
Related pages
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.
- Eaton 5E Gen2 datasheet (en-GB) (retrieved 19 October 2026)
- Eaton UK UPS buying guide (retrieved 19 October 2026)
- Eaton 3S700B product page (retrieved 19 October 2026)
- Eaton 5S550IBS product page (retrieved 19 October 2026)
- Eaton 3S Mini catalogue page (retrieved 19 October 2026)
- BSI: BS EN IEC 62040-3:2021 (retrieved 19 October 2026)
- Electrical Equipment (Safety) Regulations 2016, regulation 35 (retrieved 19 October 2026)
- GOV.UK: Electrical Equipment Safety Regulations 2016 (retrieved 19 October 2026)