Savolture · Solutions
Whole Home Battery Backup
Keep the entire house live during an outage — HVAC, well pump, kitchen, home office — sized and built right the first time.
When the grid goes down, a partial backup keeps a few lights and the fridge running. Whole home battery backup keeps the entire house live for hours or days. The gap between those two outcomes is a sizing and system-design decision you make before you buy — get it wrong and you either overspend on capacity you never use, or discover during a storm that your “backup” can’t start the air conditioner.
What “Whole Home Backup” Actually Means
Critical-Loads
A small battery powers a dedicated subpanel — fridge, some lights, internet.
Partial-Home
Most circuits except the largest loads (central AC, range, EV charging).
Whole Home
Every circuit, including high-draw appliances, sized to ride through a multi-day outage.
Rule of thumb: true whole-home backup is defined by two numbers working together — enough usable kWh to last the outage, and enough continuous and surge inverter power to run everything at once. A large battery behind an undersized inverter is still only partial backup.
How Much Battery Does a Whole Home Need?
Start from the loads you actually want to run during an outage, not your annual average. The working method:
- Add up the daily kWh of the circuits you want backed up (a typical whole-home target is 15–25 kWh/day once you trim non-essentials).
- Multiply by days of autonomy (1 day for grid backup; 2–3 for storm-prone areas).
- Divide by usable depth of discharge. LFP supports up to 90–95% DoD technically, but professional installers size to 80% DoD for daily cycling to preserve cycle life.
So a home wanting 18 kWh/day for one day needs about 18 ÷ 0.80 = 22.5 kWh of nameplate storage. See the full method in our battery sizing guide.
Quick Reference: Sizing by Home
| Home profile | Backup target | Usable need (80% DoD) | Recommended system |
|---|---|---|---|
| Small home / condo, critical loads | ~8 kWh/day, 1 day | ~10 kWh | 100Ah ×2 or one 200Ah |
| Average home, partial-to-whole | ~15 kWh/day, 1 day | ~19 kWh | 200Ah ×2 |
| Large home, true whole-home | ~22 kWh/day, 1–2 days | ~28–55 kWh | 314Ah ×2–3 |
| Storm-prone, multi-day autonomy | ~18 kWh/day, 3 days | ~68 kWh | 314Ah ×4 + solar |
The System: Battery + Inverter + Panel
Pro tip: size the inverter’s surge rating to your single largest motor load, not just the sum of running watts. A 22 kWh battery is useless during an outage if the inverter trips every time the central AC tries to start. See our hybrid inverter pairing guide.
100AhEntry / stagedView →
200AhWall-mount stapleView →
314AhHigh-density cabinetView →
UL9540Code-compliantView →
Fire Safety & Code Compliance
A whole-home system means more aggregate kWh in one location — exactly when fire-code scrutiny intensifies. Two requirements decide whether your install gets permitted:
- UL 9540 Listing — the system-level safety certification an AHJ requires to permit residential storage. Savolture’s UL9540-listed home battery is built for code-compliant permitting; see the UL9540 certification guide.
- UL 9540A fire-propagation data — required when you exceed default NFPA 855 / IFC allowances (whole-home banks routinely do). Understand the difference in our UL9540 vs UL9540A guide.
Chemistry matters: LFP has a far higher thermal-runaway threshold than NMC — one reason it is the residential standard. See LFP vs NMC. Every Savolture residential system uses LFP.
The True Cost of Whole Home Backup
Whole-home backup costs more than critical-loads backup — more kWh and a bigger inverter — but the lifetime math favors doing it right once. LFP systems rated 6,000–8,500 cycles deliver storage at roughly $0.13/kWh over their life. The expensive mistakes are buying too little capacity (and re-engineering a year later), or a battery too big for an undersized inverter (and never being able to use it). Sizing correctly up front is the single biggest cost lever.
Two Whole-Home Scenarios
Houston, TX — the AC must survive the outage
Picture a 2,400 sq ft Houston home where summer outages make central AC non-negotiable. The binding constraint isn’t daily kWh — it’s the inverter surge to start a 4-ton compressor. Pair a ~28 kWh bank (two 314Ah cabinets) with an inverter sized for locked-rotor surge.
Rural Vermont — multi-day winter outages
Consider a rural Vermont home where ice storms cut power for 2–3 days. Daily kWh and autonomy drive it: ~18 kWh/day over three days points to a large bank (four 314Ah cabinets) plus solar recharge. Aggregate capacity well above default allowances makes the UL9540-listed platform the only practical choice.
Most Common Whole-Home Backup Mistakes
Sizing the battery but not the inverter. Whole-home backup fails at the inverter’s surge limit, not the battery’s kWh. Match surge to your largest motor load.
Sizing to annual-average kWh. Backup is about outage loads. Build the load list for what you actually need to run.
Ignoring fire code until final inspection. Whole-home banks routinely exceed default allowances. Confirm UL 9540 / 9540A during plan review.
Using 100% DoD in the math. Size to 80% usable for daily cycling, or you’ll under-deliver and shorten battery life.
Whole Home Battery Backup FAQ
How many kWh do I need to back up my whole home?
Most whole-home backups target 15–25 kWh of backed-up load per day, which at 80% usable DoD means roughly 20–55 kWh of nameplate LFP storage depending on home size and days of autonomy. Size from your actual outage load list, not annual-average consumption.
Can a battery really run my central air conditioner?
Yes, if the hybrid inverter is sized for the AC compressor’s surge (locked-rotor) current, which can be 3–7× its running draw. Whole-home backup of motor loads is limited by inverter surge rating, not battery capacity.
Do I need UL 9540 for a whole-home system?
Almost always. A UL 9540 Listing is the system-level certification AHJs require. Whole-home banks often also need UL 9540A fire-propagation data because their aggregate capacity or layout exceeds default NFPA 855 / IFC allowances.
How many days of backup should I plan for?
For grid backup in stable areas, one day of autonomy is typical. In storm- or wildfire-prone regions, plan for 2–3 days and pair the battery with solar so it recharges between outages.
Is LFP better than NMC for whole-home backup?
For residential use, yes. LFP has a higher thermal-runaway threshold, longer cycle life (6,000–8,500 cycles), and better high-temperature tolerance, and produces more favorable UL 9540A results. Every Savolture residential system uses LFP.
Can I add a generator as well as a battery?
Yes. Many whole-home designs pair a battery with a generator for extended outages: the battery handles instant silent switchover and daily cycling, while the generator recharges it during prolonged events. A hybrid inverter with generator input coordinates the two automatically.
Ready to design your whole-home backup?
Send your home size, loads & target inverter
We’ll return a capacity recommendation, inverter match, and certification documentation within 24 hours.