CyberPower ST425 Review: The Pocket-Size UPS That Keeps Your Modem and Router Online
The CyberPower ST425 is a small, inexpensive standby UPS made to keep a modem, router, camera recorder or other low-power gear running through blips and short outages, and to bridge the seconds before a home generator kicks in. Buyers praise how easily it fits under a desk and how it stops the internet from rebooting every time the lights flicker. Its 260 W rating, roughly 6 minutes at half load, simulated sine wave and lack of any USB data port make it a network-gear UPS, not one for a desktop gaming PC or a computer that needs to shut itself down automatically.
- Modem and router backup
- Generator transfer gap
- Small home offices
- Tight spaces and wall mounting
Pros
- Very compact and wall-mountable
- Keeps modems and routers online through blips and short outages
- Bridges the gap until a standby generator starts
- Four widely spaced battery outlets plus four surge-only outlets
- 890 J surge protection with EMI/RFI filtering
- Three-year warranty including the battery
Cons
- Short runtime: about 6 minutes at half load
- Simulated sine wave output, not for active PFC power supplies
- No USB data port, so no automatic shutdown or monitoring
- Battery outlets are easy to confuse with the surge-only side
- Battery is not user replaceable
- Loud alarm on battery until silenced
Who is the CyberPower ST425 for?
It is for anyone whose internet drops every time the power flickers. With a 425 VA / 260 W rating, CyberPower publishes about 6 minutes of runtime at half load and 1.5 minutes at full load, but a light load such as a modem, a router and a small camera hub runs far longer: owners describe it carrying a router and modem through short outages, and one reports a 20 W mini PC lasting about two hours. People with a standby generator use it to cover the gap before the generator starts, so routers and small computers never notice the switch. At 211 x 114 x 81 mm and 3.8 lb it hides behind furniture, and keyhole slots let it hang on a wall.
What buyers love
Size and simplicity come up again and again: it is up and running out of the box in minutes, it is quiet, and it fits under a desk without taking up space. Owners with frequent power blips say the modem no longer needs minutes to reboot after every flicker, and several report it protecting a computer, router and printer through a lightning storm with repeated outages. The four widely spaced outlets take power bricks without blocking their neighbours, and buyers like the three-year warranty that covers the battery, plus CyberPower's connected equipment guarantee.
What to know before you buy
Only the four outlets on the power-button side carry battery power; the other four are surge-only, and the most common complaint from buyers whose gear shut off in an outage is that it was plugged into the wrong side. Runtime is short by design, so it is not the right UPS for a desktop with a monitor, and the simulated sine wave output can upset computer power supplies with active PFC. A minority of owners report units that could not carry even a small load when the power failed. The alarm beeps loudly on battery (a double press of the power button silences it), and there is no USB data port, no screen and no software, so it cannot tell a computer to shut down or report its status to a smart home. The battery is replaceable only by a qualified technician.
Is the CyberPower ST425 worth it?
For keeping a network online it is one of the best values in its class: a budget price, eight outlets, 890 joules of surge protection and a three-year warranty in a box smaller than a hardcover book. If you want a UPS for a desktop computer, automatic shutdown or a Home Assistant dashboard, step up to a model with a USB data port and more watts, such as CyberPower's own line-interactive units.
Frequently asked questions
How long does the CyberPower ST425 run on battery?
CyberPower rates about 6 minutes at half load (130 W) and 1.5 minutes at the full 260 W. A small load such as a modem and router runs much longer, which is the job this unit is built for.
Which outlets on the CyberPower ST425 have battery backup?
Four of the eight NEMA 5-15R outlets, on the power-button side, are battery backed and surge protected. The other four are surge protected only and lose power in an outage.
Can the CyberPower ST425 shut down my computer automatically?
No. It has no USB or serial data port, so PowerPanel software cannot read it and it cannot signal a computer, a NAS or Home Assistant. The ST625U and larger models add a USB data port.
Does the CyberPower ST425 have a pure sine wave output?
No. On battery it produces a simulated (stepped) sine wave, which suits routers, modems and most adapters but can cause problems with computer power supplies that use active PFC.
Can I replace the battery in the CyberPower ST425 myself?
CyberPower lists the battery as replaceable by a qualified technician only, not by the user. It is a 12 V / 2.9 Ah sealed lead-acid battery, and the three-year warranty covers it.
