I lost power twice in a row while working from home. The first cut lasted 90 minutes. The second lasted eight hours. My phone died, the fridge door stayed closed, and I learned that a quiet power plan beats a gas generator in my duplex.
My building rules ban fuel, and my old 500Wh battery could not carry a CPAP plus a router. I spent a weekend charting each load on paper. I lined the numbers up against models on xoolusa.com because I wanted specs I could compare without guessing. A 1000Wh battery sounds roomy, but a 300W inverter chokes on a 1440W space heater.
Start with loads, not battery size
The nameplate on my fridge says 380W. The compressor start surge hits near 700W. That surge matters more than the label. My router pulls 8W. My laptop charger reports 65W. A 100W light bar can make a dark office feel normal in winter.
I wrote down each item on a sticky note. I grouped them into two piles: keep it running and keep it lit. The first pile had the fridge, router, and CPAP. The second had a lamp, a laptop, and a small fan. That split saved me from buying a battery for things that need a few minutes of power.
Compare run time with simple math
A usable battery rarely delivers the sticker number. I assume 85% of 1000Wh is about 850Wh. If the fridge cycles at 10% duty, that is 38Wh per hour. The CPAP uses 25W. The router uses 8W. Those three parts take about 71Wh each hour, so the math points to roughly 12 hours before the battery hits a low warning.
Run time changes fast when I add one heavy plug. A 500W rice cooker can burn through half the usable store in a bit. For a storm plan, I keep the list short.
- Fridge plus router plus lamp: about 55W average, close to 15 hours on 850Wh.
- CPAP plus phone charging: about 30W, good for a night.
- Laptop plus a small fan: about 110W, near eight hours.
- Space heater: skip it. A 1500W load drains the pack in under an hour.
Think about recharge speed
A battery feels huge until it needs a refill. My old pack took 6.5 hours on wall AC. A 200W panel adds about 1.4kWh per sunny day in my yard, not the theoretical 2.0kWh. That gap matters. If I plan to run a fridge through two storm days, I need more storage before I add panel.
I also check the input port. My current unit accepts 60W from a small panel. A larger model accepts 500W. The difference turns a three-day recharge into a half-day recharge when the sun cooperates. In a garage, I run an extension cord to the unit, then put the panel in the south-facing patch near the drive.
Use real numbers, skip marketing
I do not care if a product claims “whole-home backup.” I care about three watts: the surge I must survive, the average I must sustain, and the input I can refill. I ignore the label when I plug a 120V freezer into a small station. The freezer pulls 420W steady and spikes high. It needs a bigger inverter and a cable that will not heat up.
My current setup runs a fridge, a router, and a bed-light through a normal night. It carries my laptop for four hours. The next step is a second 200W panel on the east side. That adds about 400Wh before noon. It does not turn my home into a solar farm. It buys a few more hours of quiet.
The note on my wall says: “Fridge, router, CPAP, lamp. Heater off.” That list keeps the plan simple. I keep a spare fuse, an extension cord, and a label for the inverter limit. The battery has a number, but the house needs the same number.
