How it calculates
The finder starts from a preset list, such as fridge, Wi-Fi and lights, which you can edit: change the quantity, watts or hours per day of any item, add appliances from the list or your own, and pick how long the outage lasts, from 1 day to 1 week. It then works through four steps.
- Energy you need: for each appliance, watts × hours of use per day × quantity, added up and multiplied by the number of days.
- Battery size: that energy ÷ efficiency. We assume 80% to 90% of rated capacity reaches AC appliances, so the result is a range: energy ÷ 0.90 at the low end and energy ÷ 0.80 at the high end.
- Output: the running watts of everything on the list, added together, which must stay under a station's continuous rating.
- Start-up: the largest start-up draw on the list, which must stay under a station's stated surge rating. If an appliance on the list needs 240 V, the station must supply it.
Models from our database that pass the output and start-up checks appear as cards, smallest first, in three groups: those that cover the whole range on one charge, those that come close, and those that reach it with an expansion battery. Each card shows roughly how long that model would last on your list. A note at the end explains why the other models aren't shown. The finder counts no solar or recharging during the outage.
Worked example
A load averaging 200 W for 12 hours:
- Energy: 200 × 12 = 2,400 Wh
- Low end: 2,400 ÷ 0.90 = 2,667 Wh
- High end: 2,400 ÷ 0.80 = 3,000 Wh
Under these assumptions, a station rated at 3,000 Wh or more covers it. A station between 2,667 and 3,000 Wh is borderline, and the finder groups it as close, so plan to recharge or trim the load.
Tips for an accurate result
- Enter hours of use, not hours plugged in. A light used for 5 hours a day counts as 5, even in a 24-hour outage.
- For a fridge or freezer, enter the average watts and 24 hours. Picking it from the list fills in our average.
- For a CPAP, use the hours you sleep, and check whether you'll use the heated humidifier.
- Leave a margin for appliances that draw more than their label, and check the operating temperature range in the station's manual if it will sit in a cold room or garage.
Questions readers ask
How do I find my appliances' watts?
Check the label or manual for watts, or multiply amps by volts for a rough figure. For cycling appliances such as a fridge, a plug-in power meter gives the best number.
What if no single model is big enough?
Split the load, run appliances in turns, look at a model that takes expansion batteries, or plan to recharge during the outage.
Do I need 240 V?
Only for appliances that use 240 V, such as some well pumps. Most plug-in household appliances use 120 V.
Why is a model listed as "close"?
The finder shows these models as "Close: plan to recharge." Their capacity sits between our low and high estimates, so they may cover your need, but plan a way to recharge or trim the load.