You have a 5, 10, or 16 kWh battery in mind, or already on the wall, and the question that matters is simple: how many hours will it actually run my home? The honest answer is that there is no single number, because runtime is a calculation, not a fixed property of the battery. This guide gives you the formula, worked examples for your own home, and the five reasons the real number comes in below the spec sheet. It is the reverse companion to our guide on how to choose the right size of battery: that one turns your needs into a capacity, this one turns a capacity into hours. Genixgreen has manufactured LiFePO4 storage systems in its own factory since 2011 and supplies distributors in 100+ countries, and the aim here is a calculation a dealer can hand straight to a customer.
The short answer
Runtime is your usable energy divided by your load. Usable energy is not the nameplate kWh: it is the nameplate figure multiplied by the depth of discharge and the conversion efficiency, which for a LiFePO4 system lands at roughly 85 percent of the headline. Divide that usable energy in kWh by your real load in kW and you get hours. The number is only valid with a load attached to it. A 10 kWh battery does not “last X hours” as a fact about the battery; it lasts a long time at a light load and a short time at a heavy one. So whenever you see a runtime figure, ask the only question that makes it meaningful: at what load?
The runtime formula
Here is the whole calculation in one line. The specification terms in it (usable capacity, depth of discharge, round-trip efficiency) are defined in full in our complete LiFePO4 buyer’s guide; here we only use them, and link back rather than repeat them.
Runtime (hours) = (nameplate kWh × depth of discharge × inverter efficiency) ÷ your load in kWStart with usable energy, not the nameplate kWh
A “10 kWh” battery does not give you 10 kWh of work. Two deductions stand between the label and your appliances. The first is depth of discharge: the battery management system holds a reserve to protect the cells, so a LiFePO4 unit delivers roughly 80 to 95 percent of its nameplate energy, as Battery University (BU-808) sets out. The second is conversion efficiency: turning stored direct current into the alternating current your home uses costs a few percent, so the one-way discharge (inverter conversion) efficiency typically runs around 90 to 95 percent at the system level, and this is the figure that applies to runtime, not the full charge-plus-discharge round-trip efficiency (Battery University, BU-808). Multiply the two and a sensible planning figure for usable delivered energy is about 85 percent of the nameplate: a 10 kWh battery gives you roughly 8.5 kWh to spend.
Then divide by your real load in kilowatts
Your load is the other half of the formula, and it decides everything. Capacity is measured in kilowatt-hours (kWh), the size of the tank; load in kilowatts (kW), the rate you draw from it. Divide one by the other and the same stored energy gives many hours at a low draw and few at a high one.
So how many hours, really?
Put the two halves together. Take your nameplate kWh, multiply by about 0.85 for usable energy, then divide by your load in kW. That gives a planning estimate, always read as “at this assumed load.” It is a ceiling, not a promise: the five factors later in this guide pull the real number down. It is still the right place to start.
Worked examples: the same battery, very different hours
The table below runs the formula for three common sizes at two loads: an “essentials only” load of about 0.25 kW (fridge, LED lighting, router and ONT, phone and laptop) and a heavier load of about 0.8 kW (the same essentials plus a gas-boiler circulation pump and more devices). Read every figure as “at this assumed load,” never as a fixed property of the battery.
| Battery (nameplate) | Usable delivered (~85%) | At ~0.25 kW (essentials only) | At ~0.8 kW (essentials plus heating) |
|---|---|---|---|
| 5 kWh | ~4.25 kWh | ~17 hours | ~5 hours |
| 10 kWh | ~8.5 kWh | ~34 hours | ~11 hours |
| 16 kWh | ~13.6 kWh | ~54 hours | ~17 hours |
Why the same battery shows two different numbers
Look across a single row. The 5 kWh battery runs roughly 17 hours at a light load and roughly 5 at a heavier one, a threefold difference from one product, decided entirely by what you plug into it. Runtime is a property of the battery and the load together, never of the battery alone, so a runtime figure with no load attached cannot be checked. The useful version is always conditional: this battery runs about this long at about this load.
Estimate your own load in five minutes
The table above uses assumed loads. To make it yours, you only need a rough figure for what runs at the same time during an outage. The full method for building a critical-load list, with the two-column must-run exercise, lives in our guide on how to choose the right size; here is the compact version that feeds the runtime formula.
A quick appliance-wattage method
| Appliance | Typical wattage | Notes |
|---|---|---|
| Refrigerator | 100 to 200 W | cycles on and off, so average draw is lower |
| LED lighting, several rooms | around 50 W | |
| Router and ONT | 20 to 40 W | runs continuously |
| Gas-boiler circulation pump | 50 to 100 W | critical for heating |
| Laptop and phone charging | around 100 W |
Plug your load into the formula
Add up only the items running at the same time, then divide by 1000 to get kilowatts. An apartment keeping a fridge, lights, the router, and a laptop running might sum to roughly 250 to 350 W, about 0.3 kW. A 10 kWh battery at about 8.5 kWh usable, divided by 0.3 kW, gives roughly 28 hours at that assumed load; add the boiler pump and more devices and the same battery gives far fewer. Run it for your own list and the estimate is built on your home, not a catalogue.
Five things that make real runtime differ from the headline
The formula gives a clean ceiling. The real number sits below it, and five factors decide how far below.
Usable capacity and depth of discharge
You never get the nameplate kWh. Usable energy is the nameplate multiplied by the depth of discharge, so the first and largest gap between the headline and reality is built into the battery itself, as Battery University (BU-808) explains. Size your expectations from usable energy, not from the number on the box.
Inverter conversion and standby losses
Turning stored direct current into household alternating current is not free, and the inverter also draws a small amount continuously just to stay awake. Both shorten real runtime versus a paper calculation, and a very light load does not stretch as far as simple division suggests, because the inverter’s standby draw becomes a larger share of a small load.
Cold temperature in a Ukrainian winter
Temperature changes how much energy a battery can actually deliver. As the cells get colder their available discharge capacity falls, so a battery in an unheated space gives fewer usable kWh, and therefore fewer hours, on a freezing night than the same battery in a warm room, as Battery University (BU-410) explains. Discharge itself is allowed in the cold: most LiFePO4 batteries discharge down to around minus 20 °C with reduced capacity, so the battery keeps your home running. The hard limit is on charging, which must not happen below 0 °C unless the battery has a self-heating circuit that warms the cells first. For runtime, the rule is simple: keep the battery in a heated indoor space and you keep its full hours; leave it in the cold and you lose some.
Battery age and cycle degradation
A battery delivers fewer hours late in its life than when it was new. With each charge and discharge cycle, usable capacity slowly fades toward the 80 percent end-of-life point that the industry uses to define a battery’s rated lifespan, as Battery University (BU-808) sets out, so an older unit gives noticeably fewer hours at the same load than a new one, while still working past that point and simply storing less. LiFePO4 is the slowest mainstream chemistry to fade, which is part of why it is the standard for daily-cycled home storage, as Battery University (BU-205) notes, but plan for the number to drift down over the years.
Surge and startup loads
Motors draw a brief surge several times their running watts at the instant they start: a refrigerator compressor or a pump can spike well above its steady figure for a second or two. It barely touches runtime, but it decides whether the system holds up at all. The surge sizes the inverter’s peak rating, not the runtime; an undersized inverter trips on the surge and cuts the power long before the battery is empty, which feels like terrible runtime but is really an inverter mismatch. Match the inverter to your peak load, and route any hardwired work to a qualified electrician.
How to get more hours
If the estimate is shorter than you need, there are two honest levers. Pair the battery with solar so it recharges during daylight instead of waiting for the grid, which multiplies the hours it covers across a long outage; and reduce the load by dropping non-essential appliances. If runtime is still structurally short, the real fix is capacity, not a runtime trick, and that is a sizing question our guide on choosing the right size and the pillar buyer’s guide walk in full.
Frequently asked questions
How many hours will a 10 kWh battery run my house?
It depends entirely on your load, so there is no single number. A 10 kWh battery delivers roughly 8.5 kWh of usable energy after depth of discharge and conversion losses. At an “essentials only” load of about 0.25 kW (fridge, lights, router, laptop) that is roughly 34 hours; at a heavier load of about 0.8 kW including a gas-boiler pump it is roughly 11 hours. Estimate your own load and divide 8.5 kWh by it.
How do I calculate battery runtime?
Use this formula: runtime in hours equals nameplate kWh times depth of discharge times inverter efficiency, divided by your load in kW. As a shortcut, usable energy is about 85 percent of the nameplate for a LiFePO4 system, so a 10 kWh battery gives roughly 8.5 kWh; divide that by your load and read the result as “at this assumed load.”
Why does my battery not deliver its full kWh rating?
Two deductions sit between the label and your appliances. The battery management system holds a reserve, so you use roughly 80 to 95 percent of the nameplate (the depth of discharge), and converting stored direct current to household alternating current costs a few percent more. Together they leave about 85 percent of the headline as usable energy.
Does cold weather reduce how long my battery lasts?
Yes. As the cells get colder their available discharge capacity falls, so a battery in an unheated space delivers fewer hours on a freezing night than the same battery in a warm room. Discharge still works down to around minus 20 °C with reduced capacity. Charging is the restricted action: a standard LiFePO4 battery must not be charged below 0 °C without a self-heating circuit. Keeping the battery in a heated indoor space preserves its full runtime.
Does a battery run for fewer hours as it gets older?
Yes, gradually. Usable capacity fades with each cycle toward the 80 percent end-of-life point used to rate battery lifespan, so an older unit delivers fewer hours at the same load than a new one. It keeps working past that point, simply storing less. LiFePO4 fades more slowly than other mainstream chemistries, so the drift is gentle, but plan for the runtime number to ease down over the years.
How can I make my battery last longer during an outage?
Two levers work. Pair the battery with solar so it refills during daylight rather than waiting for the grid, and switch off non-essential appliances. If runtime is still too short, the answer is more capacity, a sizing decision covered in our guide on choosing the right size.
The right next step
Runtime is a calculation you can run yourself: usable energy, which is about 85 percent of the nameplate kWh, divided by your real load in kW, read always as “at this load.” If that estimate is shorter than your outages, the fix is sizing, so start with our guide on how to choose the right size of battery, and for the full specification definitions behind the formula, see our complete LiFePO4 buyer’s guide. If you are weighing chemistries, see how LiFePO4 compares with lead-acid for backup power. To see the range, including the systems we hold in our Odesa-region warehouse for fast local supply, visit our product range. If you are a dealer or installer serving customers in Ukraine, our partners page explains how to work with us.