Trying to back up everything at once makes a power plan expensive and hard to understand. Start with functions rather than a tour of every outlet. You may need to communicate, see your way around, keep particular food cold, or operate medically necessary equipment. These needs have different consequences when power runs out.
Write the function in the left column of a page and the device beside it. “Receive local information” might mean a battery radio rather than keeping a television, router, and streaming box running. “Light the kitchen table” may be solved by a lantern rather than a whole-room lamp. Substituting a simpler tool can reduce the amount of backup power needed without losing the function.
Separate uninterrupted needs from occasional use
A phone can often be charged at intervals. Other equipment may need continuous power or a controlled shutdown. Record that distinction before assigning a battery. For any medical device, ask the provider and manufacturer about approved backup arrangements, required runtime, and where to go if power cannot be maintained. Do not put that decision in the same casual category as an entertainment device.
For ordinary electronics, note the expected hours of use and the actual connection: USB, a standard AC plug, or a manufacturer-specific adapter. The connector tells you which output must be available. The power requirement tells you whether that output can handle the load. APC's UPS guidance stresses matching the load and the desired runtime rather than choosing from the size of the case alone.
Notice dependencies
A Wi-Fi router is not the entire internet connection. A separate modem or fiber terminal may also require power, and the provider's network can still fail. Likewise, a desktop computer may be useless for an urgent task if the monitor has no power. Group the parts required for one function before calculating the energy budget.
Write down a nonpowered alternative where one exists. A printed contact card, paper map, or flashlight can cover a narrow task without consuming a larger battery's reserve. This does not mean avoiding electronics; it makes the remaining power easier to allocate.
Give the list a stopping point
Limit the first version to the few functions you would miss most during an ordinary evening outage. Leave electric heating, large cooking appliances, and household wiring decisions for a properly assessed plan. Plugging a large load into a small backup is not a way to discover whether the ratings are conservative.
Test approved combinations in normal conditions, following the equipment instructions. Record what ran, for how long, and any setting that changed the result. Keep estimates clearly marked as estimates. When a device is replaced, revisit its row: a new laptop, router, or charger can change the connectors and power requirements even when the household's underlying need stays the same.