Battery Backup Runtime Calculator
Calculate how many hours or days your home battery or portable power station will power essential household appliances during a blackout.
Battery Capacity & Essential Loads
Battery Backup Runtime Formula
Estimated Runtime (Hours) = [Usable Battery Energy (Wh) × Inverter Efficiency %] ÷ Connected Load (Watts)- Battery Energy (Wh): Nominal capacity multiplied by depth of discharge (e.g., a 10 kWh battery at 90% DoD has 9,000 Wh usable).
- Inverter Efficiency: AC inverter conversion losses (typically 88% to 94% efficiency).
- Connected Load (Watts): Combined instantaneous wattage of backed-up circuits (e.g., refrigerator, lights, internet, CPAP).
Step-by-Step Worked Example
Calculation Steps:
How to Use This Calculator
Assumptions & Limitations
- Calculations provide informational engineering estimates and do not guarantee continuous inverter peak capacity.
- Does not model simultaneous solar recharging during daytime outage hours.
Frequently Asked Questions
Can a home battery run my central air conditioning during an outage?
Central AC units draw 3,000 to 5,000 Watts and require a large starting surge. A single 10 kWh battery would be drained in 2 to 3 hours by central AC. Most homeowners install soft-starters or reserve batteries for critical loads (fridge, lights, Wi-Fi, medical equipment).
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