DC mini UPS for a router and ONT: voltage, plugs and runtime

Your router barely sips power, yet a brief outage still sends it through a full reboot. A small DC UPS can keep that little box awake without adding a full-size battery tower. The trick is buying the right electrical match before chasing the biggest battery.

Choose the TalentCell SL3400 USB-C revision for several compatible low-power devices, or the SL3402-32 for more stored energy and a wider choice of DC outputs. If your device requires regulated 12 V, keep its original power brick and use an AC UPS. Both TalentCell packs’ nominal 12 V outputs vary from 9–12.6 V: your equipment must accept that entire range.

Specs from the makers, checked October 25, 2026; runtimes below are calculated estimates.

Quick picks: buy the outputs you actually need

Multiple nominal-12 V connections: TalentCell SL3400. Its four 12 V sockets share a 4 A maximum. The current USB-C revision also provides a 9 V output and USB-A/USB-C charging, with 97.2 Wh of stored energy. That socket layout is useful when several small boxes genuinely share the same electrical requirements. The current maker manual identifies the USB-C upgrade and the shared limit.

More energy and different voltages: TalentCell SL3402-32. The current maker specification gives 142.08 Wh, with separate 5, 9, nominal 12, 15, 19 and 24 V DC outputs. There is only one 12 V socket, rated up to 3 A. Pick it for its capacity and output selection, rather than expecting four copies of the SL3400’s socket arrangement. SL3402-32 maker specifications.

Specialist FTTx equipment: CyberPower DTC50U12V. This is a 50 W telecom DC UPS with an eight-pin terminal block. It belongs on a shortlist only when your equipment documents that connector, pinout and voltage range. It is a different job from plugging a barrel lead into a typical router. CyberPower’s DTC specification gives the full electrical requirements.

Compare the ports, not just the battery label

Model and fit	Maker-documented outputs, connectors and energy
TalentCell SL3400 — several matching low-power devices	97.2 Wh; four DC5521 nominal-12 V sockets, 9–12.6 V, sharing 4 A; one DC5521 9 V/2 A; USB-A and USB-C, each up to 18 W
TalentCell SL3402-32 — more energy and mixed DC voltages	142.08 Wh on current maker page; one DC5521 nominal-12 V/3 A socket, 9–12.6 V; 9 V/2 A and 5 V/2 A DC; USB-A 5 V/2 A; 15/19/24 V outputs each 1.5 A
CyberPower DTC50U12V — matched telecom equipment	50 W; eight-pin terminal block; line mode 13.6 V ±5%, battery mode 10.5–13.5 V; battery specified as 12 V/9 Ah, with no Wh figure stated

DC5521 means a 5.5 mm outer diameter and 2.1 mm inner diameter. A familiar-looking barrel plug can still have the wrong center hole or polarity. SparkFun’s power-connector guide explains why those details matter.

Socket maxima are individual limits, not numbers to add into a whole-unit continuous-power claim. Keep the SL3400’s shared 12 V limit in view, and use the supplied charger. For simultaneous loads across different outputs, get the maker’s total continuous-load allowance for the exact revision.

The SL3400 manual specifies USB-C at 18 W maximum but does not list its negotiated voltage profiles. Don’t treat that port as a documented 12 V PD supply or assume a passive USB-C-to-barrel cable will create the voltage you need.

Read your router’s power brick: the five-minute fit check

Turn the brick over. That tiny label is your shopping list.

1. Read OUTPUT, not INPUT. The mains input describes what the charger takes from the wall; the output describes what your device receives. Write down the DC voltage.
2. Match the permitted voltage range. A device marked only “12 V” needs further maker documentation before you feed it 9–12.6 V. A regulated-input requirement points you toward the original brick plus an AC UPS.
3. Match current capacity. A replacement supply needs enough output current for the device’s requirement, including startup. A 12 V, 1 A brick has a 12 W output ceiling; that does not mean the router constantly consumes 12 W. Add the requirements of devices sharing an output group.
4. Match polarity. Compare the center-pin polarity symbols on the device and UPS output documentation or labels. Don’t assume center-positive from the plug’s appearance; ask the maker when the marking is missing.
5. Match the physical connector. Check outer diameter, inner diameter and insertion length. A tip adapter changes fit, not voltage or polarity. Keep each cable labeled with its intended device and output.

Do this for the ONT as well as the router. They can need different voltages and connectors even when they sit beside each other. Keep provider-managed equipment in place; you’re choosing its backup supply, not replacing the optical endpoint.

Runtime: turn watt-hours into a useful plan

Use this energy calculation:

Estimated hours = battery Wh × assumed usable fraction ÷ device watts

For the table, the assumed usable fraction is 85%. The load references are maker-stated maximums: 8 W for MikroTik’s hAP ax lite and 3.5 W for Ubiquiti’s UF-LOCO, or 11.5 W combined. These examples describe energy demand; they do not establish cable or voltage compatibility with either pack. MikroTik load specification · Ubiquiti load specification.

Reference load	SL3400, 97.2 Wh	SL3402-32, 142.08 Wh
Router reference — 8 W	10.33 hours	15.10 hours
ONT reference — 3.5 W	23.61 hours	34.51 hours
Both reference loads — 11.5 W	7.18 hours	10.50 hours

These are calculated estimates, not measured runtimes. Conversion losses, battery age, cutoff voltage and changing load affect the result. Use the Wh printed on your exact unit: the older SL3402 family manual lists a different nominal energy for the 32 variant, while the current product page specifies 142.08 Wh.

To make the estimate yours, measure your equipment. Our plug-in power-meter guide explains the easy wall-socket route. A wall reading includes the original brick’s losses, so using it as the denominator is a conservative planning proxy, not a DC-output measurement. Measure router and ONT together if both need to stay on.

A bigger battery buys time for the connected equipment. It cannot keep an upstream provider’s unpowered equipment running. For a NAS or several AC-powered boxes, move to the portable power-station comparison or the UPS guide instead.

Pass-through: test the handover before the outage

YABO describes the SL3400 as powering devices while charging and automatically changing to battery when mains power fails. Its SL3402-32 page also claims uninterrupted changeover. Neither retained maker document publishes a numerical switchover time. SL3400 maker description.

Make that feature earn its place: fully charge the pack, connect the intended load, then disconnect the charger’s AC input. Leave the DC output cables alone. Watch the router’s uptime and the ONT’s normal status indicators. Restore mains power and repeat the check as charging resumes. A reboot on either transition means this combination hasn’t passed your acceptance test.

Repeat with all intended devices attached. Supplying the running load and refilling the battery happen together, so leave charging headroom rather than working at every socket’s maximum. Keep the pack ventilated and accessible instead of burying it under warm power bricks.

Set it up without creating a cable puzzle

• Photograph the equipment’s power labels and record each voltage, current requirement, polarity and plug size.
• Choose outputs that satisfy every requirement, including the full battery-mode voltage range.
• Charge with the supplied charger and follow the manual’s power-switch sequence. The SL3400 manual says to turn its output switch on before connecting the charger.
• Label both ends of every DC lead, especially when using different voltages on the SL3402-32.
• Run the AC-input-removal and restoration test above, then time a supervised battery run long enough to cover your intended outage window.
• Record the result and repeat the test after equipment changes. Keep the original power bricks together so you can return to them easily.

For rack organization, a PDU can tidy AC connections; it does not add battery capacity. Keep your DC backup’s charger accessible so the handover test stays easy.

The pick: electrical fit first, hours second

Choose SL3400 when you need several compatible nominal-12 V connections in one small pack. Choose SL3402-32 when its single 12 V socket and extra voltage outputs fit your equipment and you want more stored energy. Use CyberPower DTC50U12V only for a documented terminal-block match. When the voltage requirement points elsewhere, keep the original bricks and buy an AC UPS. A boringly correct power connection beats a beautifully large battery that reboots your router.

For mains power in a travel kit, our USB-C PD charger guide shows how to match a native PD host to its voltage profile and shared-port limits.