Start with how long your power is actually out
Most comparisons start with specifications. That is the wrong end. The question that decides this is how long outages last where you live, and what stops working when they do.
Batteries are limited by energy, not power. They can usually run whatever you ask, just not for as long. Generators are limited by fuel, which for natural gas is effectively unlimited.
- Outages lasting minutes to hours: battery covers it comfortably
- Outages lasting days: that is generator territory
- Sump or well pump critical: generator, sized to include it
- Nobody reliably home: generator, for the automatic start
- Home office continuity: battery, for the instant transfer
The gap nobody mentions
A standby generator does not restore power instantly. The transfer switch detects the outage, signals the generator to start, waits for it to stabilise, and then transfers. That is seconds, not minutes, but it is not seamless.
For lights and refrigeration it does not matter. For a desktop computer or networking equipment it does. A battery transfers with no interruption at all, which is why some homes end up with a small battery alongside a generator rather than choosing between them.
What each is like to live with
This is where the difference is most concrete, and it rarely appears in a specification sheet.
- A generator runs a weekly self-test, which is audible
- A generator needs annual servicing and a battery that is a consumable
- A generator produces exhaust and must sit at code clearances from windows and doors
- A battery is silent, needs no servicing, and can live in a garage or basement
- A battery paired with solar can recharge daily during a multi-day outage
Sizing is where budgets are decided
For generators, the split is between whole-home and essential circuits. A unit that runs central air and an electric range simultaneously is a large machine. Many households do better with a smaller unit plus load management, which sheds large loads when capacity is tight and restores them afterwards.
For batteries, the equivalent decision is which circuits sit on the backed-up panel. Backing up the whole house sounds appealing and is usually what makes the project unaffordable.
One rule that applies to both
Whatever you install, it connects through a transfer switch or interlock. Never through an outlet.
Back-feeding a portable generator into a dryer or range outlet energises your home wiring with no isolation from the utility network. It can kill a line worker who believes the circuit is dead. A correctly installed inlet and interlock is inexpensive by comparison and is the only safe way to connect a portable unit.