Short answer: for long, multi-day outages, a standby generator is hard to beat: a 17-20 kW unit typically costs $7,000 to $11,000 installed and runs as long as it has fuel. A home battery (about $13,500 installed for a 13.5 kWh Tesla Powerwall 3) is quiet, fume-free and can save money every day on time-of-use rates, but it covers essentials for a day or so unless solar recharges it.
Head to head
| Standby generator (17-20 kW) | Home battery (13.5 kWh) | |
|---|---|---|
| Installed cost | $7,000-$11,000 | about $13,500 |
| Runtime | As long as natural gas or propane lasts | About 1 day of essentials; longer with solar |
| Whole house incl. central AC? | Yes, if sized for it | Usually not for long |
| Noise and fumes | Engine noise, exhaust | Silent, no emissions on site |
| Upkeep | $200-$600 a year | Minimal |
| Saves money when grid is up? | No | Yes, on time-of-use or low export credits |
| Typical warranty / life | Varies by brand | About 10 years |
Generator costs from ThePricer (July 2026); battery specs and price from EnergySage.
How long will each last?
Battery: divide usable kWh by what you run. Essentials (fridge, lights, internet, furnace fan, phone charging) often draw around 0.5-1 kW on average, so 13.5 kWh lasts roughly 13-27 hours. A whole house using the U.S. average of about 28 kWh a day would drain it in under 12 hours. Full math in how long a home battery powers your house.
Generator: on a natural gas line it can run for days, limited mainly by maintenance intervals. Propane units depend on tank size.
Which fits your outages?
- Frequent short outages (a few hours): battery. It switches over instantly and silently.
- Rare but long outages (ice storms, hurricanes): generator, or battery plus solar.
- Medical equipment at home: a battery’s instant switchover is valuable; pair it with a generator if outages last days.
- Time-of-use rates or low solar export credits: a battery earns money between outages; a generator never does.
- Tight budget: a portable generator with a transfer switch, or a portable power station for essentials. See portable power stations.
Safety
Portable generators are linked to about 100 carbon monoxide deaths a year, per the Consumer Product Safety Commission (reported by U.S. PIRG). Standby units are installed outdoors with proper clearances, but still need working CO alarms inside. Batteries need professional installation and code-required clearances.
The hybrid option
Some homes combine a battery for instant, silent backup and daily savings with a smaller generator that recharges it during long outages. It costs more upfront but covers both scenarios.
FAQ
Can a battery run my heat pump? Briefly. Heating draws a lot; plan backup around a gas furnace fan or a few rooms instead.
Is there a tax credit? The federal residential credit for batteries ended after 2025; some states and utilities pay for batteries that support the grid. See are home batteries worth it.