OUTAGE ATLAS / FIELD NOTES
Router Battery Backup: How Much Capacity?
A router and modem using an assumed 18 W together need about 267 Wh of battery capacity for eight hours under the example assumptions below. Count every powered box your connection needs. A battery at home cannot prevent an outage on your internet provider’s network.
Opens the existing planner with one editable router-and-modem load for eight hours. The 18 W is an assumption, not a measured specification. Replace it with your equipment’s combined use; startup remains unknown.
Include the whole connection
You may have one combined modem/router, or a separate router and modem. A fiber connection may also need a powered ONT—the box where the fiber enters your home. Include any network switch or mesh units you need. Use one combined measurement or add separate loads, without counting the same device twice.
A power adapter’s maximum rating may be higher than normal use. A suitable meter at the AC outlet can measure the whole load; that measurement already includes the adapters’ losses.
Work out the energy for your outage
18 W × 8 hours = 144 Wh used by the devices ((18 ÷ 0.90) + 10) × 8 ÷ 0.90 ≈ 267 Wh battery capacity
The second line allows for 90% conversion efficiency, 10 W of inverter idle draw and a 10% battery reserve. All are editable planning assumptions. They are not measured values for your equipment or the listed batteries.
In the planner, edit “Router + modem” and change the outage hours. A steady load uses 100% of the outage window. If you measured devices separately, replace the combined example with your own list.
Small loads make idle draw matter
An AC inverter can use power simply by staying on. For a small network load, that can be a substantial part of the battery target. If the manufacturer supplies a reliable idle figure, change it under “Adjust losses & reserve.” See how the planner handles losses.
This planner assumes AC operation. Direct DC power needs separate checks for voltage, polarity, connector and current. A plug fitting does not establish compatibility.
Will the internet stay on without a reboot?
Capacity does not tell you how quickly a battery switches over or whether it can act as a suitable UPS. If interruption matters, check the battery and network equipment documentation. The planner does not certify UPS behavior, and your provider’s equipment outside the home may still lose power.
For the difference between energy capacity and output power, read watts vs. watt-hours.