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Battery marketing shows whole-home backup. Reality? Most homeowners only need essential backup. One battery covers the fridge, lights, and WiFi for 24-48 hours -- at one-third the cost of powering everything. Here is how to decide what is right for your home.
$8.5-17.5K
Essential Backup
1 battery
$17-30K
Expanded
2 batteries
$25-50K+
Whole-Home
3+ batteries
1 Battery
Best Value
90% of value
Not all backup is created equal. The right choice depends on what you need to power, how long your outages last, and how much you want to spend.
Batteries
1 battery
Backup Time
24-48 hours
Cost (installed)
$8,500 - $17,500
Average Draw
~0.5 kW average
What It Powers
Refrigerator, LED lights, WiFi, phone chargers, sump pump, medical devices
Best For
Most homeowners. Covers what truly matters during a power outage.
Batteries
2 batteries
Backup Time
12-24 hours (moderate use)
Cost (installed)
$17,000 - $30,000
Average Draw
~2 kW average
What It Powers
Everything above + 1-2 mini-splits, well pump, garage door opener, home office
Best For
Homeowners with well water, home offices, or hot/cold climate comfort needs.
Batteries
3+ batteries
Backup Time
4-12 hours (depends on load)
Cost (installed)
$25,000 - $50,000+
Average Draw
~5 kW average
What It Powers
Everything including central AC, electric range, EV charger, clothes dryer
Best For
Large homes, extreme climates, or homeowners who want zero lifestyle disruption.
The 90/10 Rule of Battery Backup
Essential backup (1 battery) provides roughly 90% of the practical value at about 33% of the cost of whole-home backup. The refrigerator, lights, WiFi, and phone chargers are what homeowners actually miss during an outage. Central AC and the electric dryer? Those are nice-to-haves that triple your cost.
Every appliance you add to backup drains your battery faster. Understanding wattage helps you prioritize what actually matters during an outage.
Runs intermittently, ~40W average draw
Low draw, essential for safety
Keeps communication and smart home active
Multiple devices, low continuous draw
Critical in flood-prone areas. Runs intermittently.
Life-safety priority. Size for continuous run.
Significant draw, but keeps one zone comfortable
Critical if no municipal water. High start-up surge.
Massive battery drain. Consider 1 mini-split instead.
Use sparingly during outages. Microwave is more efficient.
Skip during outages or air-dry. Huge battery drain.
Skip during outages. Charge at Level 1 (1.4 kW) if needed.
Essential loads total: ~0.3-0.5 kW
Fridge + lights + WiFi + chargers = a single battery lasts 20-48 hours. This is all most people need.
Heavy loads: 3.5-7.6 kW each
Central AC, electric range, and EV charger each consume more power than all essential loads combined.
How long each battery lasts at three different load levels. Numbers assume a full charge and no solar recharging.
| Battery | Capacity | Essential (0.5 kW) | Expanded (2 kW) | Whole-Home (5 kW) |
|---|---|---|---|---|
| Enphase IQ 5P | 5 kWh | 10 hrs | 2.5 hrs | 1 hr |
| sonnenCore+ 10 | 10 kWh | 20 hrs | 5 hrs | 2 hrs |
| Enphase IQ 10C | 10 kWh | 20 hrs | 5 hrs | 2 hrs |
| Tesla Powerwall 3 | 13.5 kWh | 27 hrs | 6.75 hrs | 2.7 hrs |
| FranklinWH aPower 2 | 15 kWh | 30 hrs | 7.5 hrs | 3 hrs |
Runtime = usable capacity / average load. Actual runtime varies with surge loads, temperature, and battery age. Numbers assume 100% depth of discharge.
This is the real game changer. With solar panels, a single battery does not just provide 24-48 hours of backup -- it can keep your essential loads running for as long as the sun shines.
During a multi-day outage, your solar panels recharge the battery each day. Essential loads (0.3-0.5 kW average) are easily replenished by even a modest 5-6 kW solar array, which produces 20-30 kWh on a sunny day. That means a single 13.5 kWh battery refills to 100% by midday, providing overnight backup with capacity to spare.
Solar recharges the battery during the day, even during grid outages
Essential loads (0.5 kW) are easily covered by daytime solar production
One battery + solar = indefinite essential backup in sunny weather
Cloudy days: battery still lasts 20-30 hours on essentials alone
6 kW Solar Array (typical)
20-30 kWh/day
Produced on a sunny New England day
Essential Load
6-12 kWh/day
Fridge, lights, WiFi, chargers (0.3-0.5 kW avg)
Net Surplus
+8-24 kWh/day
More than enough to fully recharge a single battery daily
On cloudy days, a 6 kW array still produces 8-15 kWh -- usually enough to keep essentials running and partially recharge the battery.
Each additional battery adds less practical value than the last. The first battery covers everything critical. The second adds comfort. The third and beyond add convenience.
In Massachusetts, Connecticut, and Rhode Island, your battery can earn money through the ConnectedSolutions demand response program -- regardless of whether you have one battery or three. Utilities pay you to discharge your battery during peak demand events (typically hot summer afternoons).
This income improves the ROI of any battery purchase. A single battery earning $300-$600/year over 10 years can offset $3,000-$6,000 of the purchase cost, making essential backup even more cost-effective.
| State | Program | Earning |
|---|---|---|
| Massachusetts | ConnectedSolutions | $225-275/kW/yr |
| Connecticut | ConnectedSolutions | $275/kW summer |
| Rhode Island | ConnectedSolutions | $225/kW summer |
Battery Cost (1 unit)
$10,000
Average installed cost for single battery
DR Revenue (10 yrs)
-$3,000 to -$6,000
ConnectedSolutions income (MA/CT/RI)
Effective Net Cost
$4,000 - $7,000
After demand response earnings
Plus avoided costs from spoiled food, hotel stays, and generator fuel during outages.
For storm-prone areas, the smartest setup is not more batteries -- it is one battery for instant switchover plus a generator for extended outages.
Instant switchover
No 30-second blackout while generator starts
Silent operation
No noise complaints from neighbors at 2 AM
No fuel needed
Works immediately, no gasoline or propane required
Handles short outages solo
Most outages resolve before the battery drains
Demand response revenue
Earns $200-600/yr in ConnectedSolutions states
Multi-day backup
Runs as long as you have fuel (propane or natural gas)
High-power loads
Central AC, well pump, and dryer are no problem
Recharges the battery
Generator tops off the battery for seamless overnight power
Lower cost for capacity
A 22 kW generator costs $5,000-7,000 installed vs $25K+ for 3 batteries
Proven reliability
Generators have been providing backup for decades
FranklinWH Generator Integration
The FranklinWH aPower 2 is the only battery system we install that natively integrates with a backup generator. The FranklinWH aGate manages the battery, solar, grid, and generator as a single system -- automatically starting the generator when the battery drops below a threshold and stopping it once the battery is recharged. This eliminates the need for a separate transfer switch.
Match your situation to the right backup strategy. Most homeowners fall into the first two categories.
1 battery, essential backup
Covers the fridge, lights, and WiFi through a typical utility outage. Most cost-effective approach.
1 battery, essential backup + solar recharge
Solar recharges the battery each day, making essential backup last indefinitely during sunny weather.
Generator or 3+ batteries
Multi-day outages without solar recharging drain even large battery banks. A generator is more practical.
2 batteries minimum + generator backup
Life-safety loads demand redundancy. Two batteries provide buffer while a generator handles extended outages.
No Federal Tax Credit for Batteries in 2026
The Section 25D residential clean energy tax credit expired December 31, 2025. There is no federal tax credit for standalone home battery purchases. However, batteries acquired through a third-party ownership structure (lease or PPA like Propel) may benefit from the Section 48/48E commercial ITC, which the financing company claims on your behalf, potentially reducing your cost.
Most homes need 3 or more batteries (40-45+ kWh total) for true whole-home backup that includes central AC, electric cooking, and EV charging. However, few homeowners actually need whole-home backup. A single 10-15 kWh battery covers essential loads (fridge, lights, WiFi, medical devices) for 20-30 hours, which handles 95% of power outages.
Essential or partial battery backup covers only your most critical loads during an outage: refrigerator, LED lighting, WiFi router, phone chargers, sump pump, and medical devices. This typically requires a single battery (10-15 kWh) and costs $8,500-$17,500 installed. It provides 24-48 hours of backup power for these loads.
No. A single battery (10-15 kWh) can power essential loads for 20-30 hours, but it cannot run a central AC (3,500W), electric dryer (5,000W), or EV charger (7,600W) simultaneously. Whole-home backup requires 3+ batteries and costs $25,000-$50,000+. Most homeowners find essential backup provides better value.
Runtime depends entirely on what you power. A 13.5 kWh Tesla Powerwall 3 lasts 27 hours powering essentials (0.5 kW average), but only 2.7 hours running a whole home (5 kW average). With solar panels, a single battery can keep essential loads running indefinitely during sunny days because the panels recharge the battery.
No. The Section 25D residential clean energy tax credit expired December 31, 2025. There is no federal tax credit for homeowner battery purchases in 2026. However, if you acquire a battery through a third-party ownership structure (solar lease or PPA), the financing company may claim the Section 48/48E commercial ITC, potentially lowering your costs indirectly.
For outages under 24 hours, a battery is better: instant switchover (no 30-second delay), silent operation, zero fuel costs, and no carbon monoxide risk. For multi-day outages without solar, a generator is more cost-effective. The ideal setup for storm-prone areas is one battery for instant switchover plus a generator for extended outages. The FranklinWH aPower 2 supports direct generator integration.
Yes, if your system is designed for it. Most modern solar+battery systems (Tesla, Enphase, FranklinWH) automatically island from the grid during outages and use solar to recharge the battery during the day. This makes a single battery with solar extremely practical for essential backup, as it can run indefinitely during sunny weather.
Whole-home battery backup costs $25,000-$50,000+ installed, requiring 3 or more batteries. Essential backup with a single battery costs $8,500-$17,500 and covers the loads that actually matter during an outage. For most homeowners, essential backup provides 90% of the value at roughly one-third the cost.
Yes. In Massachusetts, Connecticut, and Rhode Island, the ConnectedSolutions demand response program pays $225-$275 per kW per summer season regardless of whether you have one battery or three. A single Tesla Powerwall 3 can earn $200-$600 per year through this program, improving the ROI of even a basic essential backup system.
Prioritize in this order: (1) Medical devices like CPAP or oxygen concentrators, (2) Refrigerator and freezer to prevent food spoilage, (3) LED lighting for safety, (4) WiFi router for communication, (5) Sump pump if in a flood-prone area, (6) Phone and laptop chargers. These loads total roughly 0.3-0.5 kW average and a single battery can power them for 24-48 hours.
Use our Battery Backup Calculator to get a personalized recommendation based on your appliances, outage history, and whether you have solar. Or talk to one of our energy advisors.