For any mission-critical computer system, it’s a good idea to think about how the system will handle power outages. At the very least it’s a good idea to give the computer enough time to gracefully shut down if the power outage will last for an indefinite time. But for extremely critical infrastructure, like our home Wi-Fi, we might consider a more long-term battery backup that can let us get through the longest of power outages.

Part of why this project from [Next Builder] works so well is that most off-the-shelf routers don’t actually use that much energy. Keeping that and a modem online when the power is out only requires a few lithium batteries. To that end, three lithium ion cells are arranged in series to provide the router with between 9 and 12 volts, complete with a battery management system (BMS) to ensure they aren’t over- or under-charged and that they are balanced. The router plugs directly into a barrel jack, eliminating any switching losses from having to use an inverter during battery operation.

While [Next Builder] is a student who lives in an area with frequent interruptions to the electricity supply, this does a good job of keeping him online. If you’re planning for worse or longer outages, a design like this is easily adapted for more batteries provided the correct BMS is used to keep the cells safely charged and regulated. You can also adapt much larger UPS systems to power more of your home’s electrical system, provided you can find enough batteries.