Size Home Battery Backup Runtime During Blackouts — Free
Homeowners installing battery backup systems (Powerwall, EcoFlow, Jackery) miscalculate runtime by confusing battery capacity (kWh) with peak appliance power draw (kW).
The proof surface
Free path: the tool computes locally in this browser with no key and no account. Where an AI step helps, any free chat assistant works — free tiers exist (Google AI Studio, Groq), but plans and limits change, so check the provider's own page. No third-party service is claimed here as verified: UNCONFIRMED — model has no browsing access this session.
Why the flat version breaks
Listing essential household circuits (refrigerator, well pump, internet router, medical devices, lighting) with wattage and duty cycles computes total watt-hour consumption against battery capacity.
How to use the battery backup load board in four passes
Record usable energy capacity (e.g., 13.5 kWh Tesla Powerwall = 13,500 Wh).
Specify nameplate running watts and estimated daily operating hours during an emergency.
Determine total continuous hours of emergency power available under your selected load profile.
SAMPLE DATA, NOT A VERIFIED CLAIM: starter record calculates 48+ hours of emergency backup runtime for a 10 kWh battery powering critical circuits. Replace these values with your own source before you rely on anything.
What breaks first
Attempting to run electric heating or central AC on small batteries
Resistance heating and central AC pull 3,000–5,000 Watts, draining standard home batteries in under 2 hours.
Forgetting appliance starting surge wattage
Compressor pumps and refrigerators require 3-5x running watts for 2 seconds to start, which can trip inverter limits.
What you pay otherwise
| The usual route | What it leaves out | Cost |
|---|---|---|
| Electrical contractor load calculation fee | Professional generator/battery sizing | $200–$400 |
| Draining emergency battery prematurely | Losing critical medical or food refrigeration power | Spoiled food & safety risks |
| This page + the free battery backup load board | Computed in your tab, result on screen before you type anything | $0 |
Try the free battery backup load board right here
Load starter record and add high-wattage appliances to watch battery runtime decrease.
FIRST-LOAD · sample record filed
Take it into the free battery backup load board
The companion app runs the same logic with a numbered intake, three starter records, a stateful share link, the one-time printable layer, and the local history shelf.
Open the free battery backup load board →Keep the work if you will use it again
Complete battery runtime calculation and emergency circuit load breakdown.
The on-screen result is free and complete. The one-time layer adds a tangible file you keep.
Boundary: Provides electrical power estimates based on user inputs. Always follow manufacturer battery installation guidelines.