How Many Batteries Do You Need for 3 Days of Backup Power? (Step-by-Step Sizing Guide)

Power outages can strike at any moment, and if you are looking to stay prepared, the key question that may come to you would be how many batteries do you need for 3 days of backup power? The answer depends on several factors, including household energy consumption, battery capacity, and the efficiency of the backup system. On average, a household requires between 20kWh to 60kWh of stored energy to maintain power for three days, which roughly translates to two to six high-capacity batteries.

While traditional gas-powered generators have been the go-to option for backup power, it comes with several limitations. If you want reliable and eco-friendly backup power, then you can check out Jackery Solar Generators, which ensures you get a renewable energy source without the hassle of fuel storage or constant maintenance.

Key Takeaways

• The number of batteries needed for a 3-day backup depends on energy consumption and the appliances you prioritize, such as medical devices, refrigeration, and communication systems.
• Unlike fuel generators, solar battery solutions provide silent, maintenance-free, and eco-friendly energy, which makes them a more sustainable choice.
• Understanding parallel vs. series connections helps optimize storage capacity, voltage, and power output for longer-lasting backup.
• The total Cost of a backup power system varies based on capacity, system efficiency, and installation, but investing in solar backup provides long-term savings and energy independence.

What is Backup Power?

Backup power refers to an alternative power source that helps the residents when the primary electricity supply is unavailable. According to a January 2025 report by the U.S. Energy Information Administration (EIA), U.S. electricity customers experienced an average of 5.5 hours of power interruptions in 2022. This number rises significantly during extreme weather conditions or grid failures, leaving homeowners vulnerable.

Whether it’s a sudden power cut due to natural disasters or a prolonged blackout due to unforeseen circumstances, having a reliable backup power supply with solar charging ensures that critical household appliances and devices remain operational.

A reliable solar backup power for home systems can:

• Keep refrigerators and freezers running, which helps prevent food from spoiling.
• Maintain lighting and HVAC system, which ensures comfort and safety.
• Power medical devices are extremely crucial for individuals who rely on electronic health equipment, like CPAP machines, small ventilators, nebulizers, and more.
• Charge communication devices that allow uninterrupted access to news and emergency contacts.

Solar Batteries vs. Generators: Choosing the Best Backup Power Solution

With advancements in battery technology and the increasing affordability of solar backup power for home use, many homeowners are shifting from gas generators to solar generators. That said, several people still debate between solar battery storage and traditional fuel-powered generators. Before you choose the best backup power solution, you should first answer a few questions that would help you decide, like:

• Am I going to travel a lot? If the answer is yes, then you do not want a backup power that takes up too much space or even comes with excessive weight.
• Do I have a family member with respiratory issues? If you have, then you cannot use the fuel-based generators inside the premises as it may worsen their health.
• Do I have multiple appliances that I need to run? If the answer is yes, you will want a reliable solution that provides output for longer hours and multiple ports that would help you power emergency appliances.

Here’s a detailed comparison between solar batteries and traditional fuel-powered generators:

A solar battery backup power solution, like Jackery Solar Generator, provides several advantages over traditional generators. For instance, Jackery Solar Generator emits zero fumes and emissions, which makes them safe for indoor use. At the same time, these portable power stations are lightweight, letting you easily transport them when needed.

How Many Solar Backup Power You Need For Three Days

When you need to understand whether or not you have enough backup power for three days, you will first need to start by doing a detailed and precise assessment of your power needs. For instance, this process involves identifying the most critical appliances that must remain operational, calculating their energy consumption, and making desired adjustments to account for efficiency losses and peak demand fluctuations.

Here’s how you can methodically approach this assessment to learn how much battery backup you need for 3 days:

Step 1: Identify Essential Appliances

You should know that not all household or off-grid appliances would require backup power for an extended period of time. During an extended power outage, you will need to prioritize ultra-essential devices to ensure energy efficiency. A few of the important essentials that would require emergency solar backup power are:

• CPAP Machine (40W - 100W): Extremely important for individuals with sleep apnea.
• Nebulizer (60W - 100W): It is essential for children and adults or whoever has respiratory conditions.
• Two-Way Radio (5W - 15W): These are crucial for emergency communication.
• Medical Refrigerator (100W - 200W): These are small refrigerators used for storing temperature-sensitive medications.
• Smartphone Charging (5W - 20W): These also come in handy as they are essential for communication during power outages.

Step 2: Calculate Daily Power Consumption

Each of the above-mentioned appliances consumes a specific amount of energy per hour. In order to determine the daily consumption, you will need to find the wattage rating and multiply it by the hours they are used per day. You can even use an energy meter for precise measurement.

For instance:

• Refrigerator (150W × 8 hours) = 1,200Wh (1.2kWh)

• CPAP Machine (80W × 8 hours) = 640Wh

• WiFi Router (10W × 24 hours) = 240Wh

• LED Lights (50W × 5 hours) = 250Wh

This means that in this condition, your daily power consumption is close to ~2.3kWh.

Step 3: Calculate 3-Day Backup Power Plan

Once you have determined the daily energy usage, you can multiply it by three days to estimate the total backup power required for three days. While considering the same appliances as mentioned above:

2.3kWh/day × 3 days = 6.9kWh of total backup energy needed

Always factor in system efficiency losses and peak power requirements to ensure that you calculate reliable performance. So, if you are using a backup power supply with solar charging that has lithium-ion batteries, which has 90% Depth of Discharge (DoD), then:

6.9kWh ÷ 0.9 = 7.7kWh of battery capacity needed

Step 4: Parallel Connection vs Series Connection

Before understanding how many batteries you need for 3 days of backup power, you will need to understand whether you are going ahead with a parallel or series connection. In a parallel connection, the voltage would remain the same, but the total capacity would increase. On the other hand, a series connection will increase the voltage while keeping the same capacity.

Most lithium-ion batteries come at 12V, 200Ah. Let’s consider the common battery size to understand our three-day backup battery setup:

Parallel Connection:

• Total Energy Needed = 7700Wh
• Energy Per Battery = 12V x 200Ah = 2400Wh
• Number of Batteries in Parallel = 7700Wh/2400Wh = 3.2 or 4 (rounding it off to avoid full discharge).

Series Connection:

• For this calculation, we will connect two 12V, 200Ah batteries in series. So:
• Total Energy = 24V x 200Ah = 4.8kWh
• Batteries Required = 4 (2 series + 2 parallel)

The series connection setup is useful for reducing energy loss in transmission and is better suited for larger off-grid solar systems where higher voltages (24V or 48V) are needed. Furthermore, you can even have a hybrid setup combining series and parallel to increase voltage and capacity.

Cost Breakdown: How Much Does a 3-Day Backup Power System Cost?

Investing in a three-day backup power system would involve the consideration of multiple cost factors, including battery type, solar panels, inverters, charge controllers, and installation expenses. Additionally, a roof-mounted solar-powered backup system would involve a higher initial investment. Let’s break down the estimated Cost of a 3-day backup power system for a home using a lithium-ion battery:

Battery Cost

The number of batteries needed depends on the total energy requirement. As per our estimated calculation above, you would require 7.7kWh for a three-day backup. Now, assuming you are going ahead with a lithium-ion battery, then:

• Capacity per battery: 2.4kWh
• 4 batteries needed (parallel/series setup)
• Cost per battery: $900 – $1,500
• Total Cost: $3,600 – $6,000

Inverter Cost

You would require an inverter that converts DC power from the batteries into usable AC power for emergency household appliances. Here, the size of the inverter will directly depend on the peak power load. Let’s consider that you are going to use a 3000 - 5000W pure sine wave inverter, then it would be around $1200 - $2000.

Solar Panels

Since we are considering a solar backup power system, you will further require solar panels to recharge the batteries with solar energy. For the ongoing example:

• Power Requirement: 3kW – 5kW solar panel system
• Number of Panels: 8 – 12 panels (400W each)
• Cost per Panel: $250 – $400
• Total Cost for Solar System: $3,000 – $6,000 (including mounting & wiring)

Charge Controller & Battery Management System (BMS)

For a solar-powered system, it is highly recommended to have a solar charge controller to regulate power flow from solar panels to batteries and one BMS that will optimize battery performance.

• MPPT Charge Controller (60A – 100A): $300 – $800
• BMS (for lithium-ion systems): $250 – $600

Installation & Miscellaneous Costs

The installation cost varies among vendors and companies who will come to your location, do the inspection, and install the entire solar backup power system. Typically, professional installation would cost you around $1100 - $3000. Whereas you will need to pay roughly $500 - $1500 for wiring, mounting, and miscellaneous objects.

Total Estimated Cost for a 3-Day Solar Backup Power System:

*The above calculation is based on the average cost details available on different portals and may vary per brand, manufacturer, and capacity.

A complete 3-day backup system using lithium-ion batteries and solar power costs around $10,000 – $20,000, but if you are looking for a more affordable option that you can carry around, then you can check out Jackery Solar Generators.

Jackery Solar Generators for Backup Power

Jackery is a leading brand when it comes to solar generators, portable power stations, and solar panels. With over 5 million units in sales, Jackery stays in the front when it comes to creating solar backup power systems for those who are looking for a reliable power option at an affordable rate.

If you are looking for emergency solar backup power for 3-days, then you can check out the solar-powered generators and solar panels from Jackery. Here is one of Jackery's best-selling products that would help you power your essential appliances at the time of extended power cuts.

Jackery Solar Generator 5000 Plus

If you are seeking a high-capacity solar backup power solution, then you can check out Jackery Solar Generator 5000 Plus. This all-in-one solar backup power is designed for home backup, off-grid living, and emergency preparedness. With a large battery capacity, it can easily support multiple high-wattage appliances, including refrigerators, CPAP machines, lights, and even air conditioning units. With fast MPPT solar charging support and a smart BMS, the Jackery Solar Generator 5000 Plus provides a cleaner alternative to fuel-powered generators.

Appliance Working Hours

• CPAP Machine (60W): 67.2H
• Nebulizer (80W): 50.4H
• Two-Way Radio (10W): 403.2H
• Medical Refrigerator (150W): 26.88H
• Smartphone Charging (15W): 268.8H

Customer Review:

“The Jackery 5000 Plus is a powerful and versatile power station with a 5040Wh capacity and 7200W output, making it perfect for a variety of needs… The user-friendly display and app provide real-time data on battery usage and remaining power.” -- Kendra.

Battery Power FAQs

What is the best option for backup power?

The best backup power solution depends on your energy needs, budget, and long-term goals. Lithium-ion solar generators are ideal for long-term, eco-friendly, and silent operation with minimal maintenance.

What is emergency vs. backup power?

Emergency power refers to an immediate power source used during sudden outages to keep essential devices running. Backup power is a longer-term solution designed to sustain homes, businesses, or essential systems for extended outages.

How long will the battery backup last?

The duration of battery backup depends on the battery capacity, the power consumption of connected devices, and the depth of discharge (DoD). For example, a 12V, 200Ah battery (2.4kWh) can run a 500W appliance for about 4.5 hours before requiring a recharge.

Which UPS gives 4 hours of backup?

A UPS providing 4 hours of backup depends on wattage consumption and battery capacity. For example, a 1500VA (900W) UPS with a 12V, 100Ah battery can provide 4 hours of backup for a 200W load.

Why buy a 1000W power supply?

A 1000W power supply (PSU) is commonly used for high-performance computers, gaming setups, and power-related workstations that require stable and efficient power distribution. It is particularly useful for systems with multiple GPUs, powerful CPUs, and multiple peripherals to prevent voltage drops and system instability.

Conclusion

Power outages are unpredictable and can even last for hours or even for days. Sometimes, these power outages are caused by severe weather or grid failures, and during such hours, having a solar backup power solution would ensure that you can power critical appliances, communication systems, and certain medical devices.

If you are going forward with solar backup power, then you can check out Jackery Solar Generator. The large battery size of Jackery Solar Generator 5000 Plus provides a fume-free, noise-free, and low-maintenance backup solution, ideal for those who want backup power when needed the most.