EXCEED / BACKUP EXPLAINED / 06
How long can a home battery
keep essentials running?
It depends on the energy available when the outage starts and how quickly your home uses it.
A battery does not come with one fixed number of backup hours. The same stored energy can last much longer when fewer loads are running.
THE BACKUP LAB
Same battery.
A different kind of night.
Try a lighter or heavier load, then jump ahead to see how much energy remains.
SET THE EXAMPLE
Net energy after allowing for starting charge, any energy kept unavailable, and system losses. Not the battery’s advertised capacity.
An assumed average for the selected loads, including appliances that cycle on and off. These are not appliance ratings.
20hours
Energy-only estimate.
Power and starting limits still apply.
Jump ahead in the outage
After 6 hours, 3 kWh has been used and 7 kWh remains.
The modeled energy lasts 20 hours at the selected average use.
This does not confirm that a battery can run your equipment. Only backed-up circuits receive power. Continuous output, motor-starting demands, equipment compatibility, and system design must also be checked. Do not use this illustration to plan life-critical backup.
How this illustration works
Runtime (hours) = net energy available to loads (kWh) ÷ average combined load (kW). Remaining energy = the greater of zero and starting energy minus average load × elapsed hours. Consumption stops when the modeled energy runs out. The battery graphic shows the fraction of the starting energy remaining, not a product’s state-of-charge reading. The timeline caps at 48 hours; longer results remain visible in the number.
The model assumes a constant average load, no recharging, and that the system can support the loads. It does not model individual appliances, temperature changes, aging, start-up surges, inverter limits, outages between charging opportunities, or a particular battery product.
TWO LIMITS TO UNDERSTAND
“Can it run?” and “For how long?”
are different questions.
Power: what can run together?
The system needs to support the equipment running at the same time, including any starting demand. A long energy estimate cannot prove that an air conditioner will start.
Energy: how long can it last?
Available stored energy sets the duration at a given average load. In the lab, doubling the average use halves the duration.
START WITH PRIORITIES
Define the outage you
want to get through.
- 01
Name the must-haves.
List the actual equipment you want available: refrigeration, selected lights, communications, or other priorities. Record model information instead of assuming a typical wattage.
- 02
Choose a target duration.
Write down whether you are planning for a few hours, overnight, or a longer interruption. Identify what you could turn off to extend backup.
- 03
Review the complete system.
Ask about backed-up circuits, usable energy at the start, power limits, and how any compatible solar or generator can contribute.
Does “whole-home backup” mean everything can run indefinitely?
No. Circuit coverage does not remove energy or power limits. The actual design and what is running determine what the system can support and for how long.
Can solar extend battery runtime during an outage?
Compatible solar in a properly configured backup system may supply loads and recharge the battery when production is available. Weather, daylight, equipment limits, and home use affect the result. This lab assumes no recharging.
See how solar behaves during an outage →Why might real runtime be shorter than expected?
The outage may begin before the battery is fully charged, or household use may be higher than expected. Available capacity, conversion losses, temperature, and system settings can also affect the energy delivered.
Choose the priorities.
Then design the backup.
Bring your equipment list and target duration to an energy assessment.
Sources and scope
Tesla’s system overview distinguishes stored energy from power output, while its outage guidance explains how household use and available energy affect backup. These are manufacturer-specific references; the unbranded lab is a general arithmetic illustration. It does not claim a specific product’s performance or confirm Exceed’s supported equipment.