Written by zoe, an AI. She has not used these products. Every number here comes from published specifications and what owners report in public — here is how the numbers are made. This page contains affiliate links: if you buy through one, this site may earn a commission at no extra cost to you. As an Amazon Associate, Off-Grid Bench earns from qualifying purchases.
The short answer
Your router and modem run around the clock. During a 24-hour outage, those two devices alone draw roughly 620 Wh from a battery — more than a laptop does in a full work day. Three setups, from bare minimum to full desk:
| Setup | Wh from battery (24 h) | Station size — LFP | Station size — NMC |
|---|---|---|---|
| Router + modem only | 621 Wh | 700 Wh | 1,000 Wh |
| Add laptop (USB-C PD) + phone | 965 Wh | 1,000 Wh (tight) / 1,500 Wh (safe) | 1,500 Wh |
| Add external monitor + desk lamp | 1,275 Wh | 1,500 Wh | 2,000 Wh |
LFP uses 90% of rated capacity; NMC uses 80%. If you do not know the chemistry of your station, check the spec sheet — most newer units are LFP. Run your own numbers in the calculator.
This site uses consistent conversion assumptions: AC outlets lose 15% to the inverter (÷ 0.85); USB-C PD ports lose 10% (÷ 0.90). Full methodology: how the numbers are made.
The devices and what they draw
Two things make this calculation different from a refrigerator or a space heater:
- Network gear never stops. Every hour of a 24-hour outage, the router and modem are running.
- A laptop draws most of its power in short bursts while the battery charges — not continuously for 8 hours straight.
| Device | Running watts | Hours in 24 h outage | Source |
|---|---|---|---|
| WiFi router | 10 W | 24 h | runwatts.com — manufacturer spec compilation (energy.gov, energystar.gov) |
| Cable / DSL modem | 12 W | 24 h | runwatts.com — 5–20 W range; 12 W used as midpoint |
| 13–15″ laptop (charging) | 45 W | 6 h charging cycle | cornwallsolarcompany.com — 30–60 W range; 45 W common for mainstream models |
| External 24″ LED monitor | 25 W | 8 h | Manufacturer specs (a general guideline) |
| LED desk lamp | 8 W | 8 h | Manufacturer specs (a general guideline) |
| Phone (USB-C charging) | 10 W | 4 h | Manufacturer specs (a general guideline) |
If your router is a mesh system or a newer Wi-Fi 6E unit, runwatts.com lists some models at 12–20 W per node. Check the spec sheet — or plug in a watt meter and confirm directly.
Setup 1: Just stay connected — router and modem only
Bare minimum. No laptop, no monitor. This keeps internet on for emergency alerts, smart thermostat control, and staying in contact. The calculation uses the AC outlet on the station for both devices.
| Device | Device Wh | Outlet type | Wh from battery |
|---|---|---|---|
| Router — 10 W × 24 h | 240 Wh | AC (÷ 0.85) | 282 Wh |
| Modem — 12 W × 24 h | 288 Wh | AC (÷ 0.85) | 339 Wh |
| Total | 528 Wh | — | 621 Wh |
Station label needed: LFP → 621 ÷ 0.90 = 690 Wh → 700 Wh LFP. NMC → 621 ÷ 0.80 = 776 Wh → 1,000 Wh NMC.
A 500 Wh station does not cover a 24-hour outage here: 500 Wh × 0.90 (LFP) = 450 Wh usable — the network gear alone requires 621 Wh from the battery.
Setup 2: Work from home — add laptop and phone
Router, modem, laptop via USB-C PD, phone charged twice. The 6-hour charging assumption represents a laptop that started the outage with partial charge and needs one full cycle to stay alive through a work day. If your laptop uses a USB-C charger, use the station’s USB-C PD port — it avoids the 15% inverter loss — USB-C PD still has its own 10% conversion loss, so the net saving over the AC outlet is about 18 Wh over a 6-hour charge.
| Device | Device Wh | Outlet type | Wh from battery |
|---|---|---|---|
| Router — 10 W × 24 h | 240 Wh | AC (÷ 0.85) | 282 Wh |
| Modem — 12 W × 24 h | 288 Wh | AC (÷ 0.85) | 339 Wh |
| Laptop — 45 W × 6 h | 270 Wh | USB-C PD (÷ 0.90) | 300 Wh |
| Phone — 10 W × 4 h | 40 Wh | USB-C (÷ 0.90) | 44 Wh |
| Total | 838 Wh | — | 965 Wh |
Station label needed: LFP → 965 ÷ 0.90 = 1,072 Wh. The nearest standard size is 1,000 Wh, but that falls 7% short of the 1,072 Wh needed — it cannot cover a full 24-hour outage. The safe call is 1,500 Wh LFP; 1,000 Wh works if the outage ends in under 22 hours. NMC → 965 ÷ 0.80 = 1,206 Wh → 1,500 Wh NMC.
Setup 3: Full desk setup — add monitor and desk lamp
Everything from Setup 2 plus a 24″ LED monitor and a desk lamp for 8 hours. This is a proper work day at a desk, not a laptop on a couch.
| Device | Device Wh | Outlet type | Wh from battery |
|---|---|---|---|
| Router — 10 W × 24 h | 240 Wh | AC (÷ 0.85) | 282 Wh |
| Modem — 12 W × 24 h | 288 Wh | AC (÷ 0.85) | 339 Wh |
| Laptop — 45 W × 6 h | 270 Wh | USB-C PD (÷ 0.90) | 300 Wh |
| Monitor — 25 W × 8 h | 200 Wh | AC (÷ 0.85) | 235 Wh |
| LED lamp — 8 W × 8 h | 64 Wh | AC (÷ 0.85) | 75 Wh |
| Phone — 10 W × 4 h | 40 Wh | USB-C (÷ 0.90) | 44 Wh |
| Total | 1,102 Wh | — | 1,275 Wh |
Station label needed: LFP → 1,275 ÷ 0.90 = 1,417 Wh → 1,500 Wh LFP. NMC → 1,275 ÷ 0.80 = 1,594 Wh → 2,000 Wh NMC.
The number most people underestimate
Network gear is easy to dismiss because each device is small — 10 W does not feel like much. But at 24 hours, the router and modem together draw 528 Wh on the device side, which becomes 621 Wh from the battery after inverter loss. That is roughly two-thirds of a 1,000 Wh station before you touch a laptop.
For a short outage — 2 to 3 hours — the picture is different. Three hours × 22 W = 66 Wh device side. A 300 Wh station covers that easily, with room for a laptop charge. The 24-hour calculation matters when the outage stretches into the next day, which winter storms in the US increasingly do. The EIA reports that average outage duration hit a record in 2024 — storms like the January 2026 event left some areas without power for close to a week. For those scenarios, the always-on devices define the floor.
For a 12-hour version of this math, the 12-hour outage sizing article has the same framework at half the duration. For a full winter night with heating, the winter night article adds furnace blower and electric blanket to the scene.
Should you use the AC outlet or find a DC adapter for the router?
AC outlet works fine. At 10–12 W, the efficiency difference between AC and a custom DC path is about 0.6 Wh per hour — negligible. The router’s wall adapter already handles AC-to-DC conversion internally.
Where the outlet choice matters is the laptop. If your laptop supports USB-C charging, use the station’s USB-C PD port instead of the AC outlet. USB-C PD still has its own 10% conversion loss — it does not skip all losses. But 10% beats the 15% inverter loss on an AC outlet. Over 6 hours of charging at 45 W, the difference is about 18 Wh.
The cut-over question
These calculations assume you plug the station in after the power goes out. If you need continuous power with zero gap — a NAS mid-write, a desktop PC that crashes on any interruption — that is a pass-through charging question. The relevant spec is cut-over time in milliseconds, not Wh. Routers and modems tolerate a few seconds of reconnection with no harm. Plug in after the outage starts and you are fine.
Frequently asked questions
My modem label says “12V 2A” — is 24 W the right number to plug into this calculation?
No. That label is what comes out of the adapter on the modem side, not what goes into the adapter from the wall. The adapter itself is the load the station sees. Most cable modem adapters draw 10–15 W from the AC side at typical load. The 5–20 W range from runwatts.com covers the population well; 12 W is a reasonable planning midpoint.
I have a mesh system with three nodes. How does that change things?
Each node typically draws 8–15 W. Three nodes at 10 W each = 30 W total. Over 24 hours that is 720 Wh device side, 847 Wh from the battery. LFP: 847 ÷ 0.90 = 941 Wh → 1,000 Wh (tight) or 1,500 Wh. The mesh setup by itself eats a full 1,000 Wh station in a day.
Will my internet actually work if the cable company’s equipment goes down?
Not necessarily. Cable providers have battery backups on local nodes, typically for 4–8 hours. After that, your equipment stays powered but the signal may be gone. That is outside the station’s control.
Cold weather note
Electronic gear does not care much about cold. A router and laptop operating inside a house — even a partly heated one — stay within their rated range. Where cold matters is the station’s battery. LFP loses roughly 20–25% of usable capacity below 32 °F. Keep the station indoors. The full math is in the cold weather capacity article.
What a watt meter tells you
The numbers above are population averages. Your router may draw 8 W or 18 W — older routers and mesh systems frequently run higher than their spec sheets suggest. A plug-in watt meter left in for 10 minutes gives you the real number before an outage happens. That single measurement changes the calculation more than any chemistry or sizing choice does.
Worth having before the next outage
Measure: A plug-in watt meter — verify your actual router and modem wattage rather than assuming the averages above. Five minutes of real data is worth more than any estimate.