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How Long Will a Whole House Battery Backup Last?

How Long Will a Whole House Battery Backup Last?

Battery backup systems are an ever-improving technology that more and more homeowners want to incorporate into their lives. And with the hype about how well they work, how they save money on energy bills, and how much more electricity they supply, especially during power outages, it makes sense why people are interested.

But there are good questions you should ask before installing one: What power differences are there between a battery backup connected to the grid vs. one with solar charging capabilities? How long can a battery backup power your home during an outage? When does a battery system need to be replaced?

Since a home battery backup system is an investment, do your research and consult with an experienced battery backup installer like Revience.

In this article, our team offers a guide on what to look for between grid-charged and solar-charged battery power systems, how to calculate how long a battery can power your home during a blackout, and how long you can expect your battery investment to last.

How Long Will a Backup Battery Power a House?

How long a battery system can operate without recharging has no simple answer because there are numerous factors to account for, including:

  • Battery storage capacity when fully charged

  • Your electricity needs and consumption, especially during an outage

  • Available charging options

If your system runs only on power from the grid, your battery may have no way to recharge for the duration of the outage. Once your battery is out of juice, your energy supply will be, too.

With a battery connected to a solar station or solar panels, your battery will have the chance to recharge for a few hours every day, which can prolong your energy supply for days, even if the power outage lasts a long time.

Battery Storage Capacity

The amount of power your battery can hold is an essential factor when choosing a battery backup system. The average American household uses just over 10,000 kilowatthours (kWh) annually to power their home, which equates to around 886 kWh per month or 30 kWh per day.

With most backup batteries holding 10 kWh of power, you will need to adjust your usage slightly during an outage or combine batteries to increase the available capacity.

The typical household should be able to run on a 10 kWh battery for a full day or two without recharging if you don’t run central air conditioning.

We’ll look more closely at appliance consumption and how to calculate battery capacity based on usage further down, but central air is the largest consumer of your electric power.

Including Solar System Outputs

A 10 kWh battery that is connected to the city’s electric power grid only draws and stores power from the grid. Once the grid is down, that battery can’t recharge until the grid is operational again.

In places where power outages are rare or don’t last long, a backup battery system that only runs through the grid may be fine since it can power a home for around 24 - 48 hours, depending on usage.

However, if your home depends on more power or needs access to continuous power for longer, combining a battery backup with a solar system is your best option. Solar panels or solar systems allow you to create your own mini-power grid that recharges each day with the sun.

Solar panel systems are measured in kilowatts and show how much energy the system can produce in an hour of peak sunlight. That means that a 5 kW system can produce 5 kWh of electricity per hour if the conditions are right.

Since conditions are not always ideal, experts assume a performance ratio of 75% and expect ideal sun exposure hours to range from 3.5 to 5.5 hours a day, depending on where you live.

For example, the calculation for how much electric power a 5 kW solar system can absorb in 4 hours of peak sunlight looks like this:

5 kW solar system X 4 sunlight hours per day X 0.75 performance rating = 15 kWh per day.

In most cases, this amount of energy can recharge a backup battery for use overnight and power essential electrical systems during the day. You may even want additional battery storage because any excess power your solar system generates is lost once a battery reaches capacity.

But how much power do you use, and how much does your home really need per day in the event of an outage?

How to Calculate Your Electricity Needs

You will likely need to budget your energy consumption in an outage, even with a battery backup. That being said, the backup system can keep essential appliances and equipment (or even non-essential ones) running as long as you’ve identified how much electricity these appliances use.

As mentioned above, heating and cooling systems use up the most energy, so it may be in your best interest to calculate them separately or as an addition to your other appliance needs. We’ll calculate those last.

Other energy priorities in your home include:

  • Refrigerator

  • Kitchen appliances

  • Water heater

  • Medical equipment

  • Lights

  • TV, Internet, and other tech devices

  • Heating and cooling

The measurements in this article are generalized, so use this as a guide for estimating. You can also estimate by averaging your monthly electricity bill or by using a smart meter to monitor your usage in real time.


  • Older models from before the 2000s = 5+ kWh per day

  • Newer ENERGY STAR models = 1.16 kWh per day

Hopefully, you have an energy-efficient refrigerator and can budget around 1.5 kWh per day.

Other Kitchen Appliances

  • Electric oven = 2.3 kWh per day

  • Electric range = 1 - 1.5 kWh per day

  • Dishwasher (energy saver cycle) = 0.5 kWh per load

  • Microwave oven = 0.12 kWh per 5 minutes

  • Toaster = 0.04 kWh per use

  • Coffee maker = 0.12 kWh per brew and 0.4 kWh per hour on warmer

Even in an outage, you’ve got to eat! But try not to use electric ovens and ranges. Budget around 1 kWh per day for kitchen appliances.

If you have gas-powered stoves and ovens, your electric use for them will be significantly less, and you may be able to use them during an outage.

Water Heater

  • Electric water heater = 4 - 5 kWh per day (running 2 -3 hours)

  • Heat pump water heater (50 - 75 gallons) = 2.5 kWh per day

In an outage, cut back on hot showers and rinse the dishes in cold water. Budget about 2.5 kWh per day for your hot water heater.

Medical Equipment

  • Nebulizer = 1 kWh per hour

  • Oxygen concentrator = 0.46 kWh per hour

  • Sleep apnea machine (CPAP) = 0.2 kWh per hour

Depending on your needs, budgeting for medical equipment may need to be higher up on your list, or you may need to use a larger storage capacity than a 10 kWh battery.


  • 1 CFL/LED 38 W bulb or 150 W incandescent bulb = 0.038 kWh per hour (less per hour for smaller watt bulbs)

In simple terms, if you budget 1 kWh per day for lighting, you could power 26 bulbs for 1 hour each before hitting your allotment.

Various Technology Devices

  • Flat screen TV: LED/OLED 4K or 1080p HDTV = 0.014 - 0.18 kWh per hour

  • Plasma TV = 0.4 - 0.48 kWh per hour

  • WiFi router = 0.024 kWh per day

  • Desktop computer = 0.06 kWh per hour

  • Laptop computer = 0.02 - 0.05 kWh per hour

  • Tablet = 0.032 kWh per day

  • Gaming system = 0.3 - 0.5 kWh per hour

Calculate phone charging and the use of multiple devices running simultaneously, and budget around 2 kWh per day, which may mean cutting back on the gaming during an outage.

Heating & Cooling Appliances

  • Electric furnace (with fan) = 10.5 kWh per hour

  • Portable space heaters = 1.5 kWh per hour

  • Baseboard heater (6’ unit) = 1.5 kWh per hour

  • Central A/C = 3 kWh per hour

  • Window A/C unit = 0.73 - 1.8 kWh per hour

  • Ceiling fan = 0.025 - 0.075 kWh per hour

  • Pedestal fan = 0.03 kWh per hour

As you can see, electric furnaces and central air will use your entire stored energy supply quickly if you have only a 10 kWh battery backup system with no solar power recharging.

If you’ve been following the budget in this guide, heating and cooling only have about 2 kWh available to use, so you may have to limit yourself to fans or a space heater or invest in a larger battery storage capacity.

When Does a Battery Backup Need to Be Replaced?

The longevity of your home battery backup system depends on several factors and should be thought of when determining if and what battery system you choose.

Most lithium-ion batteries should last you many years, but the three most critical elements that will affect the efficiency of your battery are its type, its usage cycles, and environmental issues like temperature.

Battery Types

Our experts recommend using lithium-ion batteries due to their longer lifespan and efficiency. Lead-acid batteries use to be common but are bulky and heavy, have shorter lifespans compared to lithium-ion batteries, require more maintenance, and are more sensitive to temperature changes.

Lithium-ion and lithium-ion phosphate batteries (LFP), on the other hand, maintain their charge for extended periods of time due to their lower self-discharge rate. They are also easier to install, less labor-intensive to maintain, last longer, and have a wider temperature range for seamless operation.

Usage Cycles

Usage cycles are the number of times a battery discharges, and this affects both the efficiency and lifespan of your battery. Like with other tech device batteries that need to be charged, the more you use the battery, the more you shorten the lifespan of that battery.

Also, be aware of how often you deep cycle or allow your battery to discharge to a very low level because that can decrease the lifespan of the battery.

With advances in lithium-ion battery technology, these batteries have ratings that show usage cycles in the thousands. This means that depending on how frequently you use your battery backup system, you likely won’t notice a change in battery efficiency for years.


External temperatures do affect the longevity and performance of lithium-ion batteries. Since most batteries are stored in garages where there is less insulation and often no heating or cooling, it’s important to monitor the temperature.

Batteries operate best between -4 - 140℉ (-20 - 60℃) and charge best between 32 - 113℉ (0 - 45℃).

In extreme heat, lithium-ion batteries lose performance efficiency, electrodes evaporate, which decreases the battery’s storage capacity and causes a depleted lifespan, and in rare cases, can even cause the battery to become unstable, leading to thermal runaway and fire hazards.

In Minnesota, the risk has more to do with low temperatures, which can reduce the efficiency of the battery. When temperatures drop below 0℉, it slows down the battery’s ability to store and produce electricity and quickens the discharge rate.

Revience Brings Battery Backup System Solutions to Your Home

Ready to install a home battery backup system? Let the experts at Revience help you find the perfect system for your home. Plus, our team installs the system, connects it to all of your smart home systems, and helps you maintain it for years.

Never be without power again! Call our team for battery backup systems and all of your smart home solutions.