Smart Home

How to Use a Battery Bank to Protect Your Home From Outages

Guy McDowell 13-01-2016

One day, you were sitting in your office and the power went out. But your computer kept running because you have an uninterruptible power supply or UPS. A thought went through your mind. “That was cool. I wonder if I could put my whole home on a UPS?”


Yes. Yes you can. It might even be less expensive than you think. We’ll cover the basics, but a system like this should be installed by a qualified electrician. Stick with it to the end and we’ll see how you might be able to plan out this system, and save some serious money as well.

How Can I Have Battery Backup for My Whole Home?

The concept is simple. Have several batteries connected to form one big battery, more properly called a battery bank The Tesla Battery Could Change The World - But Does it Actually Save You Money? Innovation comes at a cost. One of the hopes in energy innovation is that there will eventually be a financial benefit. The Tesla battery is no different. Read More or array. Have a way to plug that bank into your home’s power supply to keep the bank fully charged. Then, have a way to use the power from the bank when the power goes out Top 10 Activities To Do When There's A Power Outage Read More . Simple, right? Yes it is simple, but is it easy? It can be.

What Do I Need?

The hardware required to create this battery backup isn’t a lot. You’ll need batteries, an inverter Road Warriors: The Essential Gadgets Read More /charger, some battery cables, an inline fuse, a battery rack, and some electrical wire. Of course there are other little bits and pieces to it, but this is just an introduction to the system. You’re best to have a qualified electrician install this. Consider this a primer so you’ll better understand what your electrician is saying.

battery backup components

When it comes to finding an electrician, try to find one with plenty of experience in this sort of thing. Battery backups and grid-tied power systems What Is Solar Energy And Why Hasn't It Taken Off? What's the big deal with solar energy? If it's really as important and necessary as so many claim it to be, why hasn't it taken over the energy industry yet? Read More are a specialization of sorts. In fact, see if you can find someone who is NABCEP certified first. NABCEP is the North American Board of Certified Energy Practitioners. Don’t be afraid to ask for references and go see some of their other work.


nabcep accredited

If this looks like something you want to do, the next thing to figure out is the specifications of all the parts needed. This depends on details about your appliances. It also depends on how you currently use electricity 5 Smart Hacks To Save Electricity In Your Smart Home he trick to saving electricity is in knowing where most of your energy is consumed. Read More . The final piece is how long you want backup when the power goes down.

How Do I Size Equipment for my Home Battery Backup?

You need to figure out some things about how your home and appliances use electricity. What you’re figuring out is the kilowatt hours, (kWh), watts (W), and amp (A) usage of all the appliances and devices in your home. You may want to start writing these numbers down. They’ll help you a lot when you start this project, and are useful for many other energy saving projects 3 Alternative Energy Home Projects That Could Slash Your Electric Bill Let’s take a look at how we can take on some simple alternative energy DIY projects and save tons of money. Read More . Since homes vary widely across the world, let’s base the calculations in this article on a sample home. In previous articles, we’ve used a 1,600 sq.ft. home located somewhere in the northeast U.S. where power usage is highest in January.



The easiest way to figure out how many kWh your home uses in a day is to look at your power bills. Find the bill that has the most electricity usage. If you’re in the north, it’ll probably be from the first three months of the year. If you’re in the south it will probably be from the peak months of the summer. Your bill should tell you what your average daily electricity usage is for that period. That will be in kWh and is a key number for this project. The average daily electricity usage for this home January is 38kWh.

You’ll also want to know how many watts your appliances use at one time. There are a few ways to figure this out. You could get the information from the nameplates of your devices, write that all down, and then add it up. But many devices don’t have a proper nameplate with all the information. The most accurate would be to get a device like the Kill A Watt EZ Electricity Usage Monitor. The example home’s appliances and devices would draw about 4400W (or 4.4kW).

P3 International P4460 Kill A Watt EZ Electricity Usage Monitor P3 International P4460 Kill A Watt EZ Electricity Usage Monitor Buy Now On Amazon $40.62

How Do I Size an Inverter/Charger for My Battery Backup?

The inverter is the device that will take direct current (DC) electricity from your batteries and convert it to the alternating current (AC) that your home’s appliances use. It’s capacity is measured in watts and volts. You’ll want an inverter that has the ability to charge your batteries too. Because your home is still tied to grid power, your inverter needs to be able to safely tie in to the grid. These types of inverters have the ability to automatically detect when the grid power drops and switch you to the batteries. That function is known as an AC auto-transfer switch.


The important number for sizing the inverter is watts. The example home draws about 4.4 kW. You may want an inverter rated higher than that…but not too much. The bigger they are, the more expensive they are.

The next important number is the battery bank voltage (VDC). This means the voltage coming from your battery bank to the inverter. How do you figure that out? A good rule of thumb is to add 12VDC for every 1000W of AC power that you’ll need. We know we need 4400W. Being just over 4,000W you can see that you’ll need 4 X 12VDC. So a 48VDC system is probably best.

We now know we need a 4.4 kW (or 4400W) 120VAC inverter 48VDC charger. That’s a mouthful, but it gives you a good point to start searching for one. Something like the Magnum 4400W Inverter/Charger should work.

Magnum Energy MS4448PAE MS-PAE Series 4400W 48VDC Pure Sine Inverter Charger; Provides multiple ports, including an RS485 communication port for network expansion, and a remote port Magnum Energy MS4448PAE MS-PAE Series 4400W 48VDC Pure Sine Inverter Charger; Provides multiple ports, including an RS485 communication port for network expansion, and a remote port Buy Now On Amazon $1,856.00


How Do I Size My Battery Bank?

A battery bank is just a collection of batteries that are connected together. It’s the battery bank that will determine how long you can run your house while the grid power is down. So you need to figure out how long you want that to be. Take stock of outages in your area over the last few years. What’s the longest outage you’ve had? Was it a freakishly long time like a few weeks due to a hurricane Free Storm Tracking Software To Get Warned Before Everyone Else Read More ? Try not to count that in to your calculations. Battery backup for a few weeks will require charging from solar panels 6 Advantages of Solar Panels You Probably Haven't Considered Solar power is becoming increasingly common among middle class consumers, with more and more people realizing the advantages of solar panels. Read More , wind turbines, generators or a combination of those. At that point, just consider going off-grid.

Solar panels on a house roof

Most people only have an outage for a few hours. . Perhaps you’re in a very rural area where it routinely takes a day or two for the service crews to arrive. Perhaps you live in the city and you’ve never had an outage longer than 4 hours. Events like Hurricane Sandy Free Storm Tracking Software To Get Warned Before Everyone Else Read More are rare, and having a backup that would cover you for a couple weeks would be ridiculously expensive. Try not to count exceptions like that into your estimate.

Hurricane Sandy

The example home is in a city, so let’s say you’re never without power more than 4 hours. But you’re cautious, so let’s use 6 hours to build in a safety margin. Let’s figure out how many kWh you need to cover 6 hours. Divide the daily kWh used by 24 to get the hourly kWh used. Then multiply that by the number of hours you need backup. 38kWh divided by 24 gives us 1.58 kWh. Multiplied by 6 hours gives us 6.33kWh.

(Daily kWh / 24h) / Backup Need in Hours = Total kWh Needed

Batteries should not be drained more than 50% in this kind of system. That means you’ll need twice as many kWh, so that becomes 12.7kWh. Yet inverters aren’t 100% efficient, so you’ll lose a percentage of that 12.7kWh to the inverter. Inverter efficiencies vary, but 85% efficiency is a reasonable number to work with. To get your final number, add the 15% inefficiency to your kWh to get 14.9 kWh. Let’s call it 15kWh for the sake of easier math. Here’s the whole formula for this calculation:

Minimum kWh X 1.15 = Total kWh

The final number we need is the Amp hours (Ah). To get that, you divide the total kWh (12.7kWh) by the voltage of the battery system that you want. You figured that out to be 48VDC.

Total kWh / VDC of Battery Bank = Ah

Your Amp hours are going to be 12700Wh divided by 48VDC. That gives you 265Ah. Now you know you need a battery bank that will give you 265Ah at 48V. So how many batteries will you need and how will they be configured? That depends on the voltage and amp hour ratings of the batteries you want to use. For this example, let’s use a 12V 100Ah deep cycle batteries. They’re common, easy to handle, and cost about $200 each.

Mighty Max Battery 12V 100AH Battery for Solar Wind DEEP Cycle VRLA 12V 24V 48V Brand Product Mighty Max Battery 12V 100AH Battery for Solar Wind DEEP Cycle VRLA 12V 24V 48V Brand Product Buy Now On Amazon $174.99

Using this type of battery, you’ll need 12 of them, costing you at least $2400. You’ll have 3 groups of 4 batteries wired in series. The 3 groups will then be wired in parallel. This will actually give you 48V and 300Ah. The diagram below shows what that will look like.

300Ah 48V Battery Bank

There’s a simple battery bank design tool over at Go and try different configurations of batteries, system voltages, and amp hours to see what other options you may have.

Can I Do This Less Expensively?

“It sounds like this is pretty expensive.”, you think. Yes, it is. The system we’ve talked about above would be around $6500 to install. For the ability to run needed medical devices, it might be worth it. If you live in a condo or a have a home owners’ association where you can’t run a gas generator, it might be worth it. But just to make sure you have some power in a power outage?

Home Dialysis NxStage

It can be done cheaper. The key is to be strict about what appliances and devices you really need during a power outage. Eliminating non-essential loads could cut your installation cost in half. If you can trim down your power needs, you may consider getting a solar-powered generator Solar Generators vs. Fuel Generators: Which One Is Best for You? Should you choose a solar or gas powered generator for power outages and camping trips? Which is most suitable for which job? Read More like the VSP 3500 watt Generator for around $3,300. The bonus with this system is that it can keep charging even when the power is out.

Solar Powered Generator- VSP 3500 watt Generator with VSP 200watt solar charger panel Solar Powered Generator- VSP 3500 watt Generator with VSP 200watt solar charger panel Buy Now On Amazon

Trim far enough and you might even be able get away with just needing a self-contained battery back-up solution, like the Energizer 2200-watt Portable Inverter Generator for around $600.

Power Solutions PSC2200 Inverter Generator, 2200-Watt Power Solutions PSC2200 Inverter Generator, 2200-Watt Buy Now On Amazon

The important point is that you can power your home with batteries during a power outage. Armed with what you’ve learned here, you can continue to research the best way for you with a greater degree of understanding. Be careful though! Once you realize you might be able to get off the grid altogether, you might just develop a whole new energy lifestyle 7 Energy Saving Technologies to Lower Your Home's Carbon Footprint The following energy saving technologies can be introduced into our homes to reduce our environmental impact. Not all will be affordable just yet, but hopefully they will all become the norm in the near future. Read More !

What do you think about building such a system in your own home? Will you hire an electrician to build one for you? Have you ever built one? Share your own experiences in the comments section below!

Image Credits: 12V 100Ah AGM SLA Deep Cycle Battery, Magnum Energy 4400 Watt 120/240V Pure Sinewave Inverter/Charger 48V MS4448PAE, MidNite Solar Surge Protection Device MNSPD-300-AC, Whistler IC-2000W 2 Gauge Power Inverter Cables, via Amazon, NABCEP Accredited, via NABCEP, Solar panels on a house roof, via Shutterstock, NASA Examines Hurricane Sandy as it Affects the Eastern U.S., via Flickr, Home Dialysis NxStage, via WikiMedia.

Related topics: Battery Life, Energy Conservation, Home Improvement.

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  1. Anton Doos
    September 8, 2019 at 2:15 am

    So after the batteries are installed and the system switches automatically if utility power goes out, how would one know when the power went out and for how long. Is there a digital device that would record the time of the outage and the amount of time the batteries where used. This could be useful in extended outages to estimate the energy time remaining.

  2. Vinny F
    June 23, 2018 at 4:55 am

    Mr. G McDowell !!
    Thanks for sharing your wisdom - much appreciated !!
    I must say the whole article from beginning to end was so riveting. - I just wouldn't get off my chair. (felt like reading a detective novel)
    informative all throughout -
    and for that I just subscribed to MUO

  3. Steve
    February 5, 2018 at 11:43 pm

    For batteries check out Vmax Solar batteries they're the best.

  4. Pierre
    January 21, 2018 at 8:55 pm

    Excellent analysis. It helps me to figure out that back up battery power would not be feasible in my house since I use an average of 88kWh per day for a total of 32000kWh per year. I regularly have power outage running for 24h.
    This would require buying shares of Tesla or all the batteries of the company!!!!!

  5. Matt Meiresonne
    February 22, 2017 at 2:57 am

    Hey Guy,

    Great article on battery banks. There's not enough info published out there on batteries + solar panels.

    Keep up the awesome work!

  6. Brennan
    February 16, 2016 at 4:22 pm

    I live in a third-world country, a country without mains power for most of it's citizens. We know a lot about solar, and off-grid systems over there.

    I just wanted to mention that in the USA, if you are doing a deep-discharge of 50% on those sealed lead-acid batteries, then plan on replacing them in around 2 years max. All Pb based chemistries are never designed for any kind or real discharge when it comes to power outages and solar applications. It's just the wrong chemistry, period.

    However the newer LFP batteries coming out are DEFINITELY what we want. Lots of deep cycles are allowed on that chemistry, without premature capacity failures, to the tune of 80% regular deep-discharges (20% of full capacity-- the energy bucket is very empty). So Elon Musk and all the others (Tesla) are definitely on the right track with these batteries for both house and ev car applications.

    If you must use Lead-Acid (also very bad for the environment later) then spec for 75% depth of discharge, not 50% as stated in this article. But a good article overall. Thanks.

    • Guy McDowell
      February 17, 2016 at 8:44 pm

      I completely agree with everything you've said.

  7. Joe Lavery
    January 19, 2016 at 7:09 pm

    Also, electrical linemen out on repair call will not look kindly on a homeowner sending juice to the street. Shut off your main breaker.

    • Guy McDowell
      January 20, 2016 at 4:42 pm

      Isn't this something that grid tie-in systems automatically do? I was sure they had to be designed to cut back flow if incoming AC is not available.

      Every electric company I've looked at has regulations that insist on this. Some even say you need to have an outside lockout that the linemen can use to prevent your battery or solar system power from leaking into the grid.

  8. Robert Ward
    January 16, 2016 at 2:42 am

    If I lived in the country, this would definitely have been done already. 2 years ago, we had an ice storm just before Christmas, 2013. Lots of folks lost their electricity, some for as much a 2 weeks. In my location, our juice flickered for a second but never stopped. So, it's not worth it.

    • Guy McDowell
      January 18, 2016 at 4:07 pm

      Maybe not yet...but a generator or a small, portable battery bank might be a good idea. You never know how an outage will affect you.

      Because of the expansive and patched together nature of the electrical grid, something happening hundreds of miles away could potentially leave you in the dark.

  9. lott11
    January 15, 2016 at 5:12 am

    Ho one more thing add a capacitor bank on the 110 AC, for the start up of any power hungry out let.
    That will help your batteries life span, last longer.
    well have fun.

    • Guy McDowell
      January 18, 2016 at 4:04 pm

      I see what you're saying. Interesting idea!

      There's a few other things that could/should be added to a system like this, like shunts and inline fuses as well. That's why something on this scale is best left to an electrician or engineer to design.

      • lott11
        January 19, 2016 at 3:32 pm

        Hello Guy McDowell.
        On the point of that it should be done by an electrician, I agree not all things can be done by most home owners.
        But like the appliance and the equipment that they purchase, that is some thing that they should take time on.
        Wild a 60”,70” plasma looks great it is not the best choice.
        An equal OLED or LED IPS TV's with out the smart features, will cost less and can give you just as much pleasure.
        I am not going to say that one brand is better than another, what dose matter is the picture screen.
        Lets face it there are only 5 companies making screens for everyone, from TV's to cell, PC and car radios.
        TV's that run on DC power are not that uncommon, but smart TV's are.
        For a few dollars less you get a DC power TV and have money to purchase an Android box that will do the same and more.
        For a few dollars more you can get a capacitor power bank with and inverter that manages 130 to 144 Volts DC.
        When you are doing some thing like this pinching pennies, is what you are looking for but not at the expense of your investment.
        Buy it once thinking of future uses and or expansions, not Penney foolish ho this will work for just now.
        I will give a simple scenario, most people have a TV, stereo, and a PC in there living room or bed room.
        That means 2 screens and 2 set of speaker and a TV tuner from the cable company.
        Now my way 1 screen 1 PC one set of speakers,
        The TV is the monitor for the PC, that plays music and Kodi to stream TV on a 5.1 sound system.
        How much money did you saved just in equipment, not including power that you saved.
        A monitor that is 40” or 32” will cost your 10 times as much as a TV with the same resolution.
        My last point is for anyone is, look at what your going to do, ask questions from someone that knows.
        Get as much information as it is possible, get at least two different points of view.
        But most of all ask if it can expand and how much, and last look at other tech from other countries and there uses.
        Then and only then make your choices.
        Well have fun, and I hope this helps someone.

        • matt
          March 19, 2017 at 10:13 am

          in some countries / regions, it can be illegal to change a lightbulb unless you are a certified electrician.

          So the blog owner was correct from a legal standpoint to advise people to get an electrician.

          Of course, people from cambodia, vietname, bali, etc, will just do it themselves.

          Sadly, I have seen solar setups, so badly done, and so dangerous, that it would not surprise me if it caused a fire, or killed someone.

  10. lott11
    January 15, 2016 at 4:54 am

    OK lest keep it simple and stupid, you know K.I.S.S.
    The problem is that no matter how you do this it is expensive.
    Lets start with the most costly, your appliances.
    Did you know that most of them run on DC power, like PC and there components, like your TV, even lights.
    If you own your home and you are thinking of doing this do not stop at one thing.
    Plan for the long term use, other wise you will loose money.
    Plan it like if you are going off the grid, then all of this will make since.
    No matter how you build it is going to cost you, time money and a learning curve.
    Start by changing you light bulbs, all on one circuit all at same DC voltage.
    This is now simpler then you think, most light are on a circuit not tide to your outlets.
    Now replace all lights to 3.5 or 6 even 12 volts DC bulbs LED, why?
    One transformer for all the lights, and you do not have to rewire anything.
    Just move the light to another box next to the one you have with AC to DC transformer 3,6,12 volts.
    There are things that will only run on 110 AC voltage, your refrigerator the washer and dryer.
    Most TV run on 12 or 24 volts DC just like the PC and monitors, there are a few that have power bricks.
    So you can work with that, a simple DC to DC.
    Now most of the industry will tell you to run a 48, 96 DC volts they will never tell you to a 130 or 144 volt system.
    The power conversion is more efficient to the inverter, less heat means more power saved.
    The batteries use will not change, just how they are arranged and more amps for storage.
    More batteries means a greater expense, but the batteries will last longer.
    Now this are not car batteries this are deep cycle batteries, like those in your laptop or cell phone.
    And lasts but not least how are you going to charge them, wind, solar, fuel cells.
    Well that is the thing do you mix and mach, or just go for short term.
    A UPS to power your fridge, another one to power you PC wild power gets reestablished.
    This are things to think off, or to make a huge change in managing your way of life.
    To be ecological sound and independent, or the status norm do as I am told.
    Think of it, and have fun.

    • Guy McDowell
      January 18, 2016 at 4:03 pm

      This is definitely a doable thing. For people that are intent on being off-grid, this is something they may consider when building their dream off-grid home.

  11. Jack
    January 15, 2016 at 4:13 am

    Pretty good primer for setting up a whole house backup power system, however you did blow a fuse on your definition of an inverter (under the section titled "How Do I Size an Inverter/Charger for My Battery Backup?"). An inverter converts the DC from the batteries to the AC necessary to power the house, whereas the charger is what is required to convert the AC power from the house (or other source) to DC in order to charge the batteries.

    • Guy McDowell
      January 18, 2016 at 3:58 pm

      Hi Jack,

      You are completely correct. I'll talk to my editor about getting that changed. Thank you! :)