title: "Whole-Home vs Partial Backup: Choosing the Right Battery Strategy" description: "Compare whole-home backup and essential-loads-only battery systems. Understand capacity requirements, costs, and trade-offs to choose the right approach." summary: "Whole-home backup powers everything during outages but costs $30,000-$60,000+. Essential-loads backup covers critical circuits for $10,000-$20,000. Here's how to choose." category: "battery" difficulty: "intermediate" updated: "2026-02-09" tags: ["battery", "backup", "whole-home", "critical loads", "sizing"] relatedTools: ["/tools/battery-runtime", "/tools/solar-sizing", "/tools/cost-estimator"] faqs:
- question: "What's the difference between whole-home and partial backup?" answer: "Whole-home backup powers every circuit in your home during an outage — including high-draw appliances like AC, dryers, and EV chargers. Partial (essential-loads) backup powers only critical circuits like lights, fridge, Wi-Fi, and medical devices."
- question: "How many batteries do I need for whole-home backup?" answer: "A typical US home uses 30 kWh/day. For whole-home backup, you need 2-4 batteries (30-50+ kWh of storage) to cover a full day, plus solar to recharge. For essential loads only, 1-2 batteries (10-20 kWh) usually suffice."
- question: "Is whole-home backup worth the extra cost?" answer: "It depends on your priorities. If you live in an area with frequent or extended outages, have medical equipment needs, or simply want seamless power continuity, it's worth it. For occasional short outages, essential-loads backup at half the cost is usually sufficient."
- question: "Can I start with partial backup and upgrade to whole-home later?" answer: "Yes! Most battery systems are modular. You can start with 1-2 batteries on essential circuits and add more later. Just ensure your inverter and wiring are sized for future expansion."
- question: "Do I need a smart panel for whole-home backup?" answer: "Not strictly required, but a smart panel (like Span) makes whole-home backup much easier by eliminating the need for a critical loads subpanel and allowing dynamic circuit prioritization during outages."
The Backup Decision
When adding battery storage, one of the biggest decisions is: How much of your home do you want to back up?
The two main approaches are:
- Essential-loads (partial) backup: Power only critical circuits during outages
- Whole-home backup: Power everything, as if the grid never went down
Essential-Loads Backup
What It Covers
A typical essential-loads setup backs up:
- Refrigerator/freezer
- Lights (select circuits)
- Wi-Fi/router and phones
- Medical equipment
- Garage door opener
- A few outlets for charging
What It Doesn't Cover
- Central air conditioning (2-5 kW continuous)
- Electric stove/oven
- Clothes dryer
- EV charger
- Pool pump
- Electric water heater
Requirements
- Battery capacity: 10-20 kWh (1-2 batteries)
- Cost: $10,000-$20,000 installed
- Runtime: 12-24+ hours for essentials
- Installation: Requires a critical loads subpanel
Whole-Home Backup
What It Covers
Everything. Your home operates normally during an outage — AC runs, you can cook, charge your EV, do laundry. Neighbors won't even know the power is out.
Requirements
- Battery capacity: 30-60+ kWh (2-4+ batteries)
- Cost: $30,000-$60,000+ installed
- Runtime: Depends heavily on usage; 8-24 hours typical
- Power output: 15-30 kW peak to handle startup surges
- Installation: May require a smart panel or significant electrical work
Cost Comparison
| | Essential Loads | Whole Home | |---|---|---| | Batteries needed | 1-2 | 3-4+ | | Battery cost | $8,000-$16,000 | $24,000-$48,000 | | Installation | $2,000-$4,000 | $4,000-$12,000 | | Total | $10,000-$20,000 | $30,000-$60,000+ | | Runtime (no solar) | 12-24 hours | 8-16 hours | | ITC savings (30%) | $3,000-$6,000 | $9,000-$18,000 |
When to Choose Essential-Loads Backup
- Budget is a primary concern
- Outages are rare or short (under 12 hours)
- You have gas appliances for heating/cooking (less electric dependency)
- Starting with batteries and may expand later
When to Choose Whole-Home Backup
- Frequent or extended outages (wildfire zones, hurricane areas)
- All-electric home (no gas backup for HVAC/cooking)
- Medical equipment or special needs
- Remote location where generator isn't practical
- Home is the primary workspace (remote work)
The Hybrid Approach
Many homeowners take a middle path:
- Start with essential loads (1-2 batteries)
- Add a smart panel (like Span) for flexible circuit management
- Expand later by adding batteries as budget allows
A smart panel lets you dynamically choose which circuits get power during an outage, giving you more flexibility than a fixed critical-loads subpanel without needing full whole-home battery capacity.
Solar + Battery Sizing
With solar panels recharging your batteries daily, the capacity equation changes:
- Essential loads + solar: 1-2 batteries can run indefinitely during outages (solar recharges during the day)
- Whole home + solar: Need enough solar to recharge batteries AND power daytime usage. Typically 8-12 kW of solar for whole-home backup sustainability