Sizing a home battery without the guesswork
The scope question is already settled — a Duracell system backs your whole panel. What is left is duration, and here is the arithmetic you can do at your kitchen table tonight.
Sizing conversations used to start with an argument about which circuits deserve to stay on. That argument is over. The Duracell system backs your whole main service panel — everything in the house, no exclusions, no subpanel — so scope is not a variable you get to trade against budget. Duration is.
Capacity vs. power
Capacity is kilowatt-hours (kWh) — the size of the tank. It sets how long the house runs.
Continuous power is kilowatts (kW) — the size of the pipe. It sets how much can run at the same moment.
Both still matter, but they are questions about the equipment rather than about you: the system has to be able to start your compressor and hold enough energy to be worth having. What you contribute to the arithmetic is how much your house actually uses.
The kitchen-table arithmetic
This is not a list to choose from. Everything here is covered either way. It is how you reason about the clock:
| Load | Rough draw |
|---|---|
| Refrigerator | 100–200 W average |
| Chest freezer | 50–100 W average |
| Internet + router | 20–40 W |
| LED lighting, a few rooms | 60–150 W |
| Well pump | 700–1,500 W while running |
| Mini-split (one room) | 500–1,200 W |
| Central A/C | 2,500–5,000 W, more at startup |
Add the average draws for whatever your house realistically runs during an outage. Multiply by the hours you want to cover. That is your capacity target in watt-hours; divide by 1,000 for kWh.
Run it twice — once for a careful house on a mild day, once for a house running air conditioning in August. Those two numbers are the honest range, and they are usually further apart than people expect.
Where the estimate goes wrong
- Startup surge. Motors — compressors, well pumps, garage doors — pull several times their running draw for a moment. The battery has to survive that instant, not just the average.
- Depth of discharge. You do not get 100% of the nameplate kWh. Read the usable figure, not the headline one.
- Standby losses. The system itself uses a little power just being on.
- Cold and heat. Capacity is specified at comfortable temperatures. A garage in August is not that.
What we do on the visit
We read your actual consumption off your bills rather than a table of averages, and we check the panel and the service to confirm what the install involves. Your house has a real usage history; it beats every estimate on this page.
If the honest answer is that the duration you want costs more than fits your budget, we will say that plainly — the choice is how much runtime you buy, not which rooms you sacrifice.
Want this checked against your actual bill?
The call takes 30 minutes and costs nothing. We read your bill with you and put the arithmetic in writing.
Keep reading
- Why your solar bill did not go away You have panels and you are still paying the utility every month. Here is the structural reason — and the one number on your bill that tells you how big the gap is.
- Deregulated, co-op, or Entergy: how to read your Texas power bill Three lines on your bill decide whether you can shop for electricity in Texas — and whether half the offers in your mailbox apply to you at all.
- What actually happens in your house when the grid drops The order things fail in, why the second hour is worse than the first, and what a battery changes about the sequence.