Backup time is the number of hours a battery system can power a defined set of home loads during a grid outage, calculated as usable energy in kWh divided by average load in kW.
Because both inputs vary with every home and every scenario, backup time is never a fixed specification of the battery itself. The same system gives very different runtimes depending on which loads are connected.
Why it matters for home backup power
Backup time is the practical outcome that home battery sizing works toward. It connects stored energy to real demand: how many hours will the system run the refrigerator, the router, the lights, and the boiler pump before it needs a recharge? Getting this number right requires knowing both what is connected and how much energy the battery can actually deliver.
A planning mistake that recurs in sizing conversations is treating a capacity figure as a runtime. A 10 kWh battery does not deliver “10 hours of backup.” It delivers roughly 8.5 kWh of usable energy, and the hours that buys depend entirely on load. At 500 W, that is about 17 hours; at 2 kW, about 4 hours. Connecting a high-draw appliance can halve the expected runtime in minutes.(Source: Battery University BU-808)
Backup Time in practice
Key numbers
The formula: backup time (h) = usable energy (kWh) / average load (kW)
Usable energy is not nameplate capacity. For a LiFePO4 system at 80 to 95 percent depth of discharge (DoD) and 90 to 95 percent inverter efficiency, usable energy is about 85 percent of nameplate. Genixgreen LiFePO4 home systems run at a nominal 51.2 V and scale from about 5 кВт·ч to 16 kWh. On a 10 kWh system, the usable planning figure is roughly 8.5 kWh.
Load profile decides the runtime
Two homes with identical batteries get different backup times if their Критические нагрузки differ. An apartment keeping only a refrigerator, router, and lighting draws roughly 300 to 500 W; a home also running a boiler pump and several device chargers may draw 1 to 1.5 kW. Sizing for backup time therefore starts from a load audit, not from a product catalogue. Confirm the DoD setting in the system BMS before using nameplate capacity in any sizing calculation, because a lower DoD directly reduces available runtime.
How Genixgreen uses Backup Time
Genixgreen has built LiFePO4 storage in its own factory since 2011 and ships to 100+ countries, with local stock in Odesa for delivery across Ukraine. Genixgreen product specifications list nameplate and usable capacity, not a fixed backup-hours figure, because an honest runtime depends on each home’s load profile. The 6000+ cycle rating means the runtime calculation you perform at installation remains reliable for years of daily use.
Related terms
- Критические нагрузки: the appliance set whose wattage forms the denominator in the backup-time formula
- кВт·ч: the energy unit used to express both nameplate and usable capacity for the numerator
- Depth of Discharge (DoD): the fraction of nameplate capacity that is usable; a higher DoD means more runtime per cycle
- Genixgreen home battery range: systems from 5 kWh to 16 kWh with published usable capacity figures
- Full glossary: all energy storage terms in the Genixgreen glossary
Sources
- Battery University BU-808: How to prolong lithium-based batteries (DoD, usable capacity, efficiency). https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries