Quick answer
Whole-Home Battery Backup means the battery system is wired to back up your main electrical panel, so every circuit can stay live in an outage. Partial or critical-load backup feeds only a separate subpanel of chosen circuits, such as the refrigerator, lights, internet and a well pump.
Whole-home does not mean everything at once: the battery's power rating still caps how much can run together.
Quick facts
The key facts about whole-home battery backup, with sources:
- Whole-home
- Backs up the main panel; all circuits available
- Partial / critical-load
- Backs up a subpanel of chosen circuits
- One Powerwall 3
- 11.5 kW continuous, 185 LRA load start 1
- One IQ Battery 5P
- 3.84 kVA continuous, up to 48 A LRA 3
- One FranklinWH aPower 2
- 10 kW continuous, 185 A LRA 4
- Stacking limit in code
- 20 kWh per unit; 40 or 80 kWh aggregate by location (2021 IRC R328 / NFPA 855) 5
Key takeaways
- Whole-home backup wires the battery to the main panel. Partial backup feeds only a subpanel of chosen circuits.
- Whole-home does not mean everything at once. The battery's kW rating still caps what runs together.
- Big motors such as central AC and well pumps decide the design, through their start-up surge (LRA).
- Whole-home often needs more units, load controls or a panel upgrade. Partial costs less and lasts longer per kWh.
- In long outages, a trimmed load plus solar recharging matters more than which design you pick.
What "whole-home" really means
The words describe the wiring, not the result. In a whole-home design, the battery's switch sits between the utility and your main panel. When the grid fails, every breaker in the house still has power behind it.
In a partial design, only some circuits move to a separate subpanel that the battery feeds. The rest of the house goes dark in an outage, by plan.
Makers market whole-home ability. Tesla says one Powerwall 3 "can support the power needs of most homes" 1. That is a claim about power. Whether it holds for your home depends on your loads.
Sources: [1]
How the two designs are wired
- Whole-home: grid → islanding switch or gateway → main panel → every circuit
- Partial: grid → main panel → islanding switch → critical load panel → chosen circuits
- Both: battery and solar → inverter → the panel behind the switch
Why power, not storage, decides it
A main panel can draw far more than one battery can deliver.
A 200 A, 240 V service is rated for 48 kW in theory (200 × 240), while one Powerwall 3 supplies 11.5 kW continuous and one IQ Battery 5P supplies 3.84 kVA.
Normal homes rarely draw anywhere near the service rating, but a central AC, an electric range and a dryer running together can exceed one battery.
Motor start-up is the second test. Tesla lists a load start capability of 185 locked rotor amps per Powerwall 3; Enphase lists up to 48 A LRA for the IQ Battery 5P and notes it "may vary". Compare those with the LRA on your air conditioner's or well pump's nameplate.
So "whole-home" quotes usually come with one of three answers: more power from extra units, smart breakers or load controllers that shed big loads automatically, or both.
Whole-home vs partial backup
| Whole-home backup | Partial (critical-load) backup | |
|---|---|---|
| What is wired to the battery | The main service panel | A new or existing subpanel fed by the battery |
| Which circuits work in an outage | All of them, up to the power limit | Only those moved to the subpanel |
| Battery power needed | Enough to start your largest motor while the rest of the house runs | Enough for the chosen circuits |
| Typical hardware | More battery units, a whole-home gateway, often smart load controls | Fewer units and a critical load panel |
| Day-to-day experience | Nothing to think about until loads exceed the limit | Unbacked rooms go dark; you planned which ones |
| Main risk | Overload trip if big loads coincide | Forgetting a circuit you need, such as a sump pump |
Example: what stacking units adds
Arithmetic on published figures only. Real systems may limit combined output; check the maker's design guide with your installer.
| Setup | Continuous power | Stored energy | Fits the 80 kWh garage/outdoor cap? 5 |
|---|---|---|---|
| 1 × Powerwall 3 | 11.5 kW 1 | 13.5 kWh | Yes |
| 4 × Powerwall 3 (the most Tesla supports) | 46 kW (4 × 11.5) | 54 kWh (4 × 13.5) | Yes, but above the 40 kWh indoor-room cap |
| 2 × aPower 2 | 20 kW (2 × 10) 4 | 30 kWh | Yes |
| 6 × aPower 2 (up to 15 allowed per aGate) | 60 kW | 90 kWh | No, without UL 9540A data or another location |
The maker's limit and the code limit are different things. Whole-home designs that stack many units can run into the code cap before the maker's cap.
Where each design fits best
- Whole-home: homes where central AC, an electric range or a well pump must run in an outage, and owners who do not want to pick circuits ahead of time.
- Partial: homes whose must-run loads fit one battery, and long-outage areas where stretching kWh matters more than comfort.
- Either: homes with solar that can refill the battery each day.
Whole-home backup: gains and costs
Whole-home gains
- Every room keeps power; no guessing which outlets work.
- No need to move circuits to a subpanel.
- Can run big loads like central AC if the kW and LRA ratings allow.
Whole-home costs
- Usually more units or load controls, so a bigger quote.
- Drains the battery faster, since more loads can run.
- Risk of an overload trip when big loads start together.
- More stored kWh can hit code caps by location 5.
Limits of whole-home backup
Whole-home backup does not add hours. If the whole house can draw power, it often does, so the same kWh runs out sooner. For outages that last days, that matters. The EIA found major events drove nearly nine of the 11 average outage hours in 2024 8.
Heat also trims power. Tesla says Powerwall 3 output may be de-rated above 40°C (104°F) 1, which can bite on the hot afternoons when AC demand peaks.
What drives the cost of whole-home backup
HyreSolar does not print prices without dated quotes. The cost drivers are clear, though. NLR splits home battery cost into the pack, the battery inverter, other hardware, labor, permits and interconnection, sales and profit 7. Whole-home designs push up nearly every line.
Ask whether a quote includes a whole-home gateway, smart load controls, a main-panel or service upgrade, and extra permit drawings.
Warranty. Each unit carries its own warranty. Tesla: 70% capacity at 10 years, unlimited cycles for backup and solar use 2. FranklinWH: 15 years or 60 MWh throughput 4.
A decision rule, step by step
- List the loads you cannot be without in an outage, and their running watts and start-up LRA.
- If they fit inside one battery's continuous kW and surge rating with room to spare, partial backup does the job at lower cost.
- If you need central air, an electric range or an EV charger on backup, price whole-home with load management and check the surge figure against each motor.
- Size the kWh last, against how long your outages run and whether solar can recharge each day.
- Have the installer confirm the total kWh fits the code cap for where the units will go.
The battery sizing calculator runs the kW and kWh checks with your loads.
Living with whole-home backup
- In an outage, avoid starting big loads together: run the dryer after the AC cycles off.
- Use load controls or app alerts if your system has them.
- Before a storm, set a higher reserve or storm mode; FranklinWH lists charging fully ahead of severe weather 4.
- Keep the system online for updates and alerts 1.
Warning signs and when to call a pro
- The system trips to off when the AC or pump starts.
- Lights dim hard or flicker in backup.
- The battery empties in hours on a normal evening load.
- The main breaker or gateway area is hot, buzzing or smells.
- Call the installer. Never bypass the gateway or swap breakers to "fix" a trip.
Safety rule
Whole-home backup changes your main panel wiring. Only a licensed electrician should do it, under a permit.
Code limits that shape whole-home designs
Under the 2021 IRC R328 and NFPA 855 Chapter 15, as UL summarises them, each unit is capped at 20 kWh.
Totals are capped at 40 kWh in utility closets, basements and storage rooms, and 80 kWh in garages, accessory buildings, on outside walls or outdoors.
Units sit 3 feet apart unless UL 9540A data supports less 5.
States can amend these. California's 2022 residential code, as one city's handout shows, allows higher totals outdoors in some setups and requires a heat alarm in attached garages with batteries 6. South Carolina enforces the 2021 codes 9. Ask which edition and amendments your permit uses.
Whole-home backup vs related terms
| Term | What it means | How it differs |
|---|---|---|
| Whole-home backup | Battery behind the main panel | — |
| Battery backup | Any battery power in an outage | Wider term; includes partial |
| Critical load panel | A subpanel of chosen circuits | The core of partial backup |
| Standby generator | A fuel generator that starts on its own | Runs as long as fuel lasts; see battery vs generator |
| Battery capacity | kWh stored | Sets hours, not what runs at once |
Misconceptions
- Myth Whole-home means I can run everything at once.
- Reality All circuits are live, but the kW rating still caps how much runs together.
- Myth Whole-home lasts longer.
- Reality Usually the opposite: more loads can run, so the same kWh drains faster.
- Myth More units are always allowed.
- Reality Codes cap total kWh by location, such as 40 kWh in a utility room 5.
Whole-home backup in SC, GA and VA
Outage length is a real variable here: EIA reports South Carolina customers averaged nearly 53 hours without power in 2024, the longest of any state 8.
For outages measured in days, a partial-backup system with solar recharging often outlasts a whole-home system with the same kWh, because it spends less energy per hour.
Summer heat in the Southeast makes central AC the load most people want, and the one most likely to need extra kW. Georgia and Virginia counties set their own code editions.
Which should you choose?
- Pick partial if your must-run loads fit one battery and you value runtime over comfort.
- Pick whole-home if central AC or other large loads must run, and you accept more units or load controls.
- In long-outage areas, plan solar recharging either way.
- Next step: get both designs priced side by side, with the kW, LRA and kWh math shown.
Next steps
Questions about whole-home battery backup
How many batteries do I need to back up my whole house?
Enough continuous kW and surge to run your biggest coincident loads, then enough kWh for your outage length. For many homes with central air, power, not storage, is what pushes the count above one unit. Codes also cap total kWh by location, which can shape where extra units go.
Is a critical load panel required for partial backup?
Partial backup needs some way to separate the backed-up circuits, usually a subpanel. Some systems use smart breakers or controllers instead. Your installer's design and the permit drawings show which. Either way, decide your must-run circuits before the electrician starts.
Can a whole-home battery run central air conditioning?
Only if its surge rating covers the compressor's locked rotor amps and its continuous rating covers the running load alongside everything else. Check both numbers before relying on it. Powerwall 3 and FranklinWH aPower 2 each list 185 LRA; one IQ Battery 5P lists up to 48 A LRA.
Is whole-home backup worth it over partial?
It is worth it when you need large loads such as central air in an outage and accept the extra units and controls. If your essentials fit one battery, partial backup lasts longer per kWh and costs less. In long-outage areas, runtime often matters more than comfort.
Can one battery back up a whole house?
Sometimes. Tesla says one Powerwall 3 can support the power needs of most homes, with 11.5 kW continuous. Whether it works for yours depends on which big loads run together and their start-up surge. A load list with nameplate amps settles it.
What is load management in whole-home backup?
Load management means smart breakers or a controller that switch off lower-priority loads, such as a water heater or EV charger, when demand nears the battery's limit. It lets a smaller battery support whole-home wiring without tripping. Some makers require it for whole-home setups.
Does whole-home backup need a new electrical panel?
Not always. It depends on your panel's rating, space and condition, and how the battery connects. Some homes need a main-panel or service upgrade. Our panel upgrade check gives a first read; a licensed electrician makes the final call.
How long does whole-home backup last?
Divide usable kWh by your average load in kW. Because every circuit is live, the load is often higher than with partial backup, so runtime is shorter. Solar can refill the battery each day. Trimming loads during a long outage stretches it further.
Sources
- Tesla, Powerwall 3 Datasheet (2024), retrieved .
- Tesla, Powerwall Limited Warranty (USA), effective 21 August 2023, retrieved .
- Enphase Energy, IQ Battery 5P data sheet (DSH-00010-11.0-EN-2025-05-06), retrieved .
- FranklinWH, aPower 2 data sheet (2025), retrieved .
- UL, 2021 Residential ESS Requirements (IRC R328 and NFPA 855 Chapter 15 summary, 2021), retrieved .
- City of Monte Sereno (CA), Residential Energy Storage Systems building requirements (7/2024), retrieved .
- National Laboratory of the Rockies (NLR, formerly NREL), Annual Technology Baseline 2024: Residential Battery Storage, retrieved .
- US EIA, Today in Energy: Hurricanes in 2024 led to the most hours without power in the United States in 10 years (1 December 2025), retrieved .
- SC Building Codes Council, code adoption, retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Power, surge, stacking and warranty figures from the Tesla, Enphase and FranklinWH data sheets and Tesla US warranty.
Code limits from UL's summary of 2021 IRC R328 / NFPA 855, with a 2024 California city handout as an example of state amendments; outage data from EIA; cost structure from the NLR ATB.
The 48 kW and stacking figures are arithmetic on published ratings, not measured loads or maker-confirmed system outputs.
Suggest a correction. We fix errors and say what changed.