How Long Will A Backup Battery Power My Home During An Outage?

As power outages, heat waves and wildfires continue to impact California every year, it’s important to know how long a backup battery will power your essential appliances. Depending on the severity of the situation, homeowners can be without power for hours or even days. A high-quality home battery can provide enough power to keep your lights on, refrigerator running, and other appliances operational during an outage.

But the real question is how long a backup battery will power your home during these outages. The answer depends on several factors, including:

  • The appliances you want to power (and for how long),
  • the power rating of your home battery,
  • the usable storage capacity of your battery,
  • whether your battery is paired with solar panels.

Let’s dive into each of these factors and find out how long a backup battery can power your home during outages, blackouts and more.

Factors That Impact How Much of Your Home a Battery Can Power

In order to determine how much of your house you can power with a home battery, some things to take into consideration are: how much power you need and how much power your battery supplies in kilowatts (kW).

Which Appliances Do You Want to Back Up?

To determine how much power you need, you first need to figure out which or your appliances you want to back up. You most likely don’t run every home appliance every day, so you’re also less likely to run them all at once. As a result, your battery installer will work with you to calculate how much power is required for different appliances in your home.

Home batteries provide power ratings in kW, so if you know the power draw of each appliance you want to run during an outage, you can calculate the power requirements for each. If you don’t know these power draw totals, check out the US Department of Energy’s appliance load calculator.

When you determine each appliance’s wattage, you can then calculate the power requirements to back up your home. For example, it may take 200 watts to power a refrigerator, 20 watts per light bulb, 300 watts for the TV, etc.

Energy-efficient appliances (such as those with an ENERGY STAR label) can help with energy savings. We also put together a comprehensive list of energy-efficient appliances and other energy savings strategies for your home. If you don’t want to do the research and calculations on your own, your Solar Technologies energy consultant can help you evaluate your options. 

What Is The Power Rating Of Your Battery?

Once you calculate how much power is needed to back up some or all of your home, you can determine which energy storage system would be best for you.

The SunPower SunVault home battery and Tesla Powerwall both have continuous power ratings that represent the amount of power (in kilowatts) your battery can steadily provide. This metric determines how many appliances can run simultaneously for extended periods of time. Most home batteries have a continuous power rating between 5 to 8 kilowatts, which could power a handful of appliances at the same time.

Here are the continuous power ratings for each:

SunVault Home Battery Technical Details

  • Power rating: 6.8 kW
  • Rated energy capacity: 13 kWh per battery

Tesla Powerwall Technical Details

  • Power rating: 5.8kW continuous
  • Rated energy capacity: 13.5 kWh per battery

Factors That Impact How Long You Can Power Your Home With a Battery

To determine how long a battery can power your home, factors to consider include your battery’s usable storage capacity, along with which appliances you’re using and for how long. Whether your home battery is paired with a solar panel system and if you’re including any load management systems with your storage system are also important.

Your Battery’s Usable Storage Capacity

The first factor to consider is how much energy your battery can store, which is the usable storage capacity or rated energy capacity. This metric is measured in kilowatt-hours (kWh) since it represents how much power of electricity (kW) your battery uses over a certain time frame (hours).

Based on the SunVault and Powerwall usable storage capacity rates above, if your SunVault has 13 kWh of usable storage capacity, you could either use 6.5 kilowatts of power for 2 hours (6.5 kW * 2 hours = 13 kWh) or 1 kW for 13 hours. In the same way cell phones and computers lose charge when you’re doing more with the device, your home battery will as well.

Which Appliances You Use and For How Long

Once you know your battery’s usable capacity and how much power your appliances consume, you can plan for which ones to use and how long you’ll be able to use them during an outage. For example, if your battery’s usable capacity is 10 kWh, you can power:

  • your 3,500 W heat pump for under 3 hours;
  • your 300 W TV for 33 hours;
  • your 200 W refrigerator for 50 hours;
  • your 25 W phone charger for 400 hours;
  • Or your 6 W WiFi router for 1,600 hours.

Since multiple appliances will likely run at the same time, it makes the backup power calculation more important with many tradeoffs and options. If you have your TV on for two hours during an outage for example, that’s three less hours you can power your refrigerator. However, if you plan to keep only your essentials running during an outage (like phones, computers, your fridge, etc), you can expect a 10kWh battery (or more) to keep those appliances running for nearly 24 full hours.

Whether or Not Your Battery is Paired with Solar Panels

When you install a standalone battery in your home, you’ll have backup power to begin with but can’t recharge the battery until grid service is restored. If you experience frequent, but short, outages, a standalone battery is a great option to power your home while the power is out. For homeowners that experience outages for longer durations (that last a day or more), a standalone battery won’t provide the backup power you need.

When you pair solar panels with battery storage, you can supply power to your home indefinitely with the power of the sun. Even after a few cloudy days, once the sun shines again (as it always does in California), your battery will recharge and keep your home powered even if your neighbors are stuck in the dark.

How to Calculate How Much and How Long Your Home Can Run on a Battery

In general, a battery with a continuous power rating of 5 kW will power a number of appliances at once, such as:

  • a refrigerator (800 W to start it, 200 W to run it),
  • furnace fan for gas heat (at 600 W),
  • cell phone chargers (at 25 W each),
  • a WiFi router (at 6 W),
  • a dozen light bulbs (21 W per light bulb, or about 250 W in total),
  • a TV (at 300 W), and
  • even a microwave (at 800 W) or coffee pot (at 900 W).
  • Depending on other appliances you’re running, you might even be able to run your washing machine (800 W) or a dishwasher (1800 W). 

Finally, you’ll need to take into consideration how long you plan to use each appliance. The longer your appliances stay on, the less stored energy you’ll have to power other appliances during the night or until the next sunny day. For instance, keeping the TV on all day uses more than 7 kWh of electricity a day, which is a significant amount of the 10 kWh of usable energy storage most home batteries have.

For greater peace of mind protection during outages, many homeowners installing backup power systems are opting for two home batteries instead of one for greater backup capacity. It truly depends on how much power your home uses, how big it is and even the weather in your area. 


Whichever battery backup you choose to power your home during an outage, rest assured it’s a smart choice as climate change continues to worsen the impact of natural disasters, wildfires and more. Adding a home battery or pairing it with your solar panel system is a great way to keep the lights on during outages.

If you’re ready to change the way you power your home and start saving more with solar, contact us for a free customized solar quote.

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