The short answer
Portable generators run on gas/propane fuel ($1.50/kWh, multi-day capable). Battery backup systems are silent and indoor-safe ($0/kWh ongoing, 12-24 hours capacity). Generators win for 3+ day outages; batteries win for short outages. Generators MUST run 20+ ft from house — CO killed 90+ Americans during 2024 outage events.
Backup power for a US home splits into two camps: portable generators (gas or propane, 2-7 kW typical, $400-$1,200) and battery backup systems (lithium-ion, 5-30 kWh capacity, $1,500-$15,000). Generators run for as long as you can supply fuel; batteries hold finite energy. Generators produce carbon monoxide; batteries are silent and indoor-safe. This guide walks the cost-per-kWh comparison and the safety rules each requires.
Portable generator — fuel-fed, multi-day capable
Portable generators run on gasoline, propane, or dual-fuel. 5-7 kW is typical residential — enough to power refrigerator, lights, internet, sump pump, and a window AC unit simultaneously. Cost: $400-$1,200 for the generator + $50-$150 for transfer switch.
Fuel consumption: a 5 kW generator running half-load uses ~0.6 gallons/hour gasoline. At $3.50/gallon, that is $50/day. A 3-day outage costs ~$150 in fuel.
Lifespan: well-maintained portable generators last 10-15 years. Need annual oil changes, monthly test runs, fuel stabilizer in storage gas, proper winterization.
Battery backup — silent, indoor-safe, finite capacity
Battery backup systems (Tesla Powerwall, Enphase IQ Battery, LG Chem RESU, Generac PWRcell) range from 5-30 kWh capacity. A 13.5 kWh Powerwall powers essential loads for 12-24 hours.
Cost: $1,500-$15,000 installed. The federal residential clean energy credit expired Dec 31 2025, so 2026 installs no longer qualify. State incentives (CA SGIP, MA Connected Solutions, NY NYSERDA) range from $200-$3,500 per battery.
Lifespan: 10-15 years with 70-80% capacity retention. Indoor-safe (no CO, no fuel). Requires solar or grid charging. The solar-battery-backup-cost-payback guide covers payback math.
Infographic
Multi-day outage cost — generator vs battery
Safety — CO, fire, and the 20-foot perimeter
Generator CO safety: 20+ feet from any window, door, or vent. Never indoors. CO killed 90+ Americans during 2024 outage events alone. CO detectors with battery backup on every floor.
Generator fire safety: gas-powered units run hot. Allow 30 minutes cool-down before refueling. Never refuel while running. Store gas in approved containers, away from house.
Battery fire safety: lithium-ion batteries are stable but rare thermal-runaway events have occurred. Install per manufacturer spec (clearances, ventilation). Indoor installations require local code compliance.
Recap
Bottom line
For most US households the choice between portable generator and battery backup comes down to outage duration expectation. Generators handle multi-day outages indefinitely if fuel is available but require strict CO safety practices (20+ feet from home, never indoors). Batteries handle 12 to 24 hours of essential loads silently and indoor-safe but cost 5 to 10 times more upfront and run out when the battery does.
For households in storm-prone regions with frequent multi-day outages (Gulf Coast, Florida, parts of Northeast), a generator is the practical baseline. For households in mild climates with rare brief outages, a battery (especially paired with solar) provides clean backup without fuel logistics. The how-to-prepare-for-power-outage and solar-battery-backup-cost-payback guides cover the broader outage-preparedness framework.
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