Build your exact appliance list and find out precisely how much battery you need — and how long a Powerwall, Franklin, or Enphase battery will run your home.
Quick answer
Essential loads (fridge, lights, router, phone charging) draw 400–600W and use 10–14 kWh/day — one 13.5 kWh Powerwall covers 24+ hours. Add central AC and daily demand jumps to 36–48 kWh, requiring 3+ batteries for full-day backup.
Reviewed 2026-07-26
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Quick Answer
Essential loads (fridge, lights, router, phone charging) draw 400–600W and use 10–14 kWh/day — one 13.5 kWh Powerwall covers 24+ hours. Add central AC and daily demand jumps to 36–48 kWh, requiring 3+ batteries for full-day backup.
Source: Wattcrunch methodology and cited primary data
Why generic battery sizing guides fail you
Most solar websites say things like "a Powerwall is good for 1–2 days of backup." That's meaningless without knowing what you're running. A home with medical equipment, a sump pump, and window AC units has a completely different backup requirement than one with just a fridge and router. This calculator sizes your battery to your actual home.
The case for separating critical from comfort loads
The fastest way to dramatically extend your battery runtime is to identify which loads are truly critical during an outage versus which are comfort items. Your refrigerator, router, phone chargers, and lights are critical. Your dishwasher, dryer, and window AC are not — at least for the first 24 hours. Most homeowners can cover genuine critical loads with a single 13.5 kWh battery for 2–3 days.
Solar + battery: the recharge advantage
Unlike a generator, a solar+battery system can recharge automatically every day during an outage. An 8 kW solar system generating 32 kWh on a clear day can fully recharge two Powerwalls and power your home simultaneously. This is why the solar+battery combination outperforms a generator for multi-day outages in most US climates — fuel becomes irrelevant.
Sources behind this estimate
Wattcrunch combines user inputs with published solar-production, electricity-market, incentive, and tariff information. Use the primary references below to understand what the model can estimate and what still needs confirmation for your property.
Utility export rates, eligibility rules, and installer pricing can change. Confirm the applicable tariff, interconnection requirements, and tax treatment before making a purchase decision.
Frequently asked questions
How long will a Tesla Powerwall last during an outage?+
It depends entirely on what loads you run. A Powerwall holds 13.5 kWh of usable energy. Running just essentials — fridge (3.6 kWh/day), lights (1.4 kWh), router (0.36 kWh), phones (0.2 kWh) — totals about 5.5 kWh/day, giving you roughly 2.4 days per Powerwall. Add a window AC unit and you are down to about 14 hours.
What is depth of discharge (DoD)?+
DoD is how deeply you can drain a battery without damaging it or reducing its lifespan. Most home batteries operate at 90–100% DoD. A 13.5 kWh battery at 90% DoD delivers 12.15 kWh of usable energy. Round-trip efficiency (typically 90–95%) further reduces this slightly.
Can I run air conditioning on a solar battery?+
A standard 3-ton central AC draws 3,500W. Running it 8 hours/day = 28 kWh/day — more than two Powerwalls per day. A mini-split at 1,500W for 8 hrs = 12 kWh, which is more manageable with a single battery. Solar recharging during the day can offset much of this, but AC is the single biggest challenge for battery backup sizing.
What is the difference between critical loads and whole-home backup?+
Critical loads backup powers a sub-panel with your most important circuits: fridge, some lights, internet, and medical equipment. This is typically achievable with 1–2 batteries and is what most installers configure. Whole-home backup powers everything simultaneously, which often requires 3+ batteries and a larger inverter.
Should I get a battery or a generator?+
A battery is silent, requires no fuel, needs zero maintenance, charges from solar, and is instantly available. A generator is cheaper upfront, can run indefinitely with fuel, and handles higher loads. For typical power outages under 24 hours, a battery with solar recharge wins on total cost of ownership. For multi-day outages in disaster-prone areas, a battery plus a small generator for recharge backup is the most resilient setup.