The single biggest mistake people make when buying a backup power system is underestimating how much power they actually need. They buy a unit that's perfect for a camping trip, only to find it can't even run their refrigerator for more than a few hours during a real outage.
Before you spend a single dollar, you need to do a "power audit." It sounds complicated, but it's a simple, 10-minute calculation that will save you from a very expensive mistake.
Step 1: Inventory Your "Must-Have" Appliances
Grab a pen and paper and walk around your house. List everything you absolutely need to keep running during an extended outage. Be realistic. You don't need the TV, but you absolutely need the refrigerator.
Your list should look something like this:
- Refrigerator/Freezer
- Internet Modem & Router
- A few lights (e.g., in the kitchen and bathroom)
- Phone / Laptop chargers
- Medical devices (if any, like a CPAP machine)
- Sump pump (if you have one and it rains)
Step 2: Find the Wattage of Each Device
Every electronic device has a label that lists its power consumption in watts (W). It's usually on the power brick or on the back of the appliance. Sometimes you'll see volts (V) and amps (A) instead. If so, just multiply them: Volts × Amps = Watts.
Here are some typical numbers:
- Refrigerator: 150-200W (but needs 1000-2000W to start up!)
- Modem & Router: 10-15W
- LED Light Bulb: 8-12W
- Laptop Charger: 65W
- Phone Charger: 10-20W
- CPAP Machine: 30-60W
Add up the running watts for all the devices you plan to use at the same time. For example: Refrigerator (200W) + Modem (15W) + 2 Lights (20W) + Laptop Charger (65W) = 300W total running watts.
Step 3: Factor in Runtime to Get Watt-Hours (Wh)
Now you know how much power you need at any given moment. Next, you need to figure out how long you need to run it. This gives you the battery capacity you need, measured in watt-hours (Wh).
The formula is simple: Running Watts × Hours = Watt-Hours
Using our 300W example, if you want to get through a 10-hour outage: 300W × 10 hours = 3,000Wh
This is a big number! But remember, your fridge doesn't run constantly. It cycles on and off. A good rule of thumb is that a fridge runs about 1/3 of the time (or 8 hours a day).
Let's recalculate for a 24-hour period:
- Refrigerator: 200W × 8 hours = 1600Wh
- Modem/Router: 15W × 24 hours = 360Wh
- Lights: 20W × 6 hours = 120Wh
- Laptops/Phones: 75W × 4 hours = 300Wh
- Total needed for 24 hours: ~2,380Wh
Step 4: Choose a Power Station with a Higher Capacity
Now you have your target number: 2,380Wh. When you shop, you should look for a power station with a capacity at least 20% higher than your calculation to account for power loss and inefficiencies.
In our example, you'd want a power station with at least 2,800Wh of capacity. This puts you in the range of a large, expandable unit like the Bluetti AC200L or an EcoFlow Delta 2 with an extra battery.
By taking 10 minutes to do this math, you can shop with confidence, knowing you're buying a system that will actually meet your needs when it matters most.