The Short Answer: A home battery backup system stores electricity to power your home during a power outage. It combines a battery (or bank of rechargeable batteries), an inverter, and a transfer switch tied to your electrical grid panel. An AGM battery storage system delivers reliable backup power for essential appliances like your fridge, sump pump, and medical devices at a fraction of the cost of a lithium whole-home backup system.
According to Ready.gov, outages can cut communications, water, and transportation across whole communities, and longer outages tied to severe weather are becoming more common. A right-sized backup system gives homeowners energy independence during those events without the $15,000 whole-home price tag, and it can pay for itself in avoided food loss, saved sump pump repairs, and peace of mind.
What Is a Home Battery Backup System?
A home battery backup system charges from the electrical grid during off-peak hours (or from a solar power system) and switches to battery power during peak hours or outages. During normal operation, the battery sits topped off and ready. When the grid drops, the transfer switch senses the loss and routes stored power to your circuits, usually in a matter of seconds. Some homeowners also use their backup battery to shift energy usage away from peak hours to trim their electric bill during normal months.
The Core Components
- Battery storage system: AGM, gel, or lithium-ion batteries provide the energy storage.
- Inverter: Converts DC power to AC. A hybrid inverter also manages solar input.
- Transfer switch: Isolates the system from the utility grid during outages.
- Wiring, breakers, and fuses: Keep the install safe and up to code.
A backup system works with or without a solar system. Pairing the two lets you recharge with solar energy during the day and store excess energy for use at night, which extends your runtime during a multi-day outage.
Essentials Backup vs Whole-Home Backup
The size of the system you need comes down to how you plan to use it. Most homeowners assume they need whole-home backup, but essentials-only is often the smarter choice, both for your budget and for your install timeline.
When Essentials Backup Is the Smart Choice
Essentials backup powers critical loads: fridge, sump pump, furnace blower, well pump, lights, communications, and medical devices. Capacity runs 2 to 10 kWh at $1,500 to $5,000. It handles the outages families actually see without paying for capacity to run air conditioners you can skip for a day or two.
When Whole-Home Backup Makes Sense
Whole-home backup runs heavy loads like central HVAC and electric ranges. Capacity is 20 to 40 kWh, at $15,000 to $50,000 including professional installation. It fits remote workers, homes with medical equipment, and areas with frequent multi-day outages where partial backup will not cut it. The National Weather Service notes extreme weather is driving longer outages in more places, so match your system size to the outage pattern in your area.
Choosing the Right Battery for Home Backup
Battery chemistry drives cost, safety, and lifespan more than any other decision.
AGM Batteries
Absorbent Glass Mat (AGM) batteries are sealed and safe to install indoors, which is a big deal for anyone tucking a backup system into a basement, garage, or utility closet. Unlike flooded batteries that need regular maintenance, AGM rechargeable batteries hold charge on float for years without hands-on care, which is exactly the job a backup battery has to do.
Fullriver builds AGM in every capacity a home backup system needs. The DC Series is a premium true deep cycle option, the EGL Series is the flagship pure-lead line for the longest float life, and the Full Force Series is the value pick for cost-conscious builds.
Lithium-Ion Batteries
Lithium iron phosphate (LiFePO4) offers higher energy density and lighter weight than AGM, but costs three to five times more per usable kWh and typically requires professional installation. It makes more sense for cycle-heavy applications where the battery discharges and recharges daily, like an off-grid home tied to a large solar array. Flooded lead-acid is cheaper upfront than AGM but off-gases hydrogen during charging and is not safe for indoor installation. See our AGM vs lithium breakdown for a full comparison.
How to Size Your Home Battery Backup System
A simple three-step method covers most households and helps you avoid overbuying capacity you will rarely use.
Step 1: List Your Essential Loads
When choosing a home battery backup system, it is important to understand how much electricity your essential appliances and devices actually use. Wattage varies by model and startup requirements, but the following estimates give a general idea of the power needed for common household loads.
- Refrigerator: about 150 watts
- Sump pump: about 200 watts
- Furnace blower: about 500 watts
- Well pump: about 800 watts
- LED lighting: about 50 watts
- Router and phones: about 100 watts
- CPAP machine: about 60 to 300 watts
Keep in mind that some appliances, including refrigerators, sump pumps, and well pumps, draw extra startup power when the motor first kicks on. This surge wattage should be factored into your sizing math so the inverter and backup battery bank can handle the peak load without shutting down.
Step 2: Calculate Daily Energy Use
Multiply each device’s wattage by hours per day. A typical essentials load lands around 5 to 8 kWh per day.
Step 3: Multiply for Duration and Depth of Discharge
Multiply daily use by target outage length, then by 2 for the 50% depth of discharge that extends AGM lifespan. For 2 days of 7 kWh use: 7 × 2 × 2 = 28 kWh of storage capacity. The California Air Resources Board’s Backup Power Tool offers a free sizing calculator for your energy needs.
What Else You Need Besides the Battery
The battery is the biggest piece, but a working system needs three more parts. You need a pure sine wave inverter sized to peak load (2,000W handles most essentials), a transfer switch (manual $150 to $400, automatic $1,000+) to isolate from the utility grid, and a battery charger to keep the bank topped off between outages. Fullriver FR Series chargers and Delta-Q chargers pair with the DC, EGL, and Full Force lines and prevent both undercharging and overcharging.
Cost of a Home Battery Backup System
Costs vary widely by battery chemistry, system size, and installation method. Here is what to expect in real dollars for a typical setup:
- AGM essentials backup (DIY-friendly): $1,500 to $4,000 for a 4 to 8 kWh system.
- Lithium essentials backup: $6,000 to $12,000 for the same capacity.
- Whole-home lithium: $15,000 to $50,000 with professional installation.
- Standby generator or backup generator: $3,000 to $10,000 plus fuel and yearly maintenance. Battery energy storage systems run silent, work indoors, and never need refueling.
Explore Fullriver AGM Batteries for Your Backup System
A right-sized AGM bank keeps your essential appliances running through outages your family actually sees. For a standalone home battery, a solar battery bank tied to your solar system, or reliable backup power for critical loads, Fullriver has an option that fits. Use the Fullriver Battery Finder to match capacity to your setup, browse the DC, EGL, and Full Force lineups, or find a local dealer for hands-on guidance.
Frequently Asked Questions
How long will a home battery backup system last during an outage?
A 4 kWh AGM bank powers a typical essentials load (fridge, lights, router, sump pump) for 1 to 2 days at normal usage. Larger banks or lower loads extend runtime, and adding solar can keep essentials running indefinitely during an extended outage.
Do I need solar panels for a home battery backup system?
No. Battery banks charge from the electrical grid during normal use and switch to battery power during outages. Solar helps recharge during extended outages but is not required.
Is AGM or lithium better for a home battery backup system?
AGM is the practical choice for most homeowners. It costs less per usable kWh, is safer for indoor installation, and excels in the standby role home backup requires. Lithium fits cycle-heavy applications like daily off-grid living. To learn more, visit our blog on AGM vs Lithium batteries.
Can I install a home battery backup system myself?
Yes, for AGM systems with manual transfer switches and modest bank sizes. Panel connections and any tie-in to the electrical grid should always be handled by a licensed electrician.
