What a home battery actually
keeps running during an outage.
PG&E PSPS events hit the foothills regularly. SMUD outages happen too. A home battery switches to backup mode automatically and keeps your critical loads running. Here's what that actually means: which appliances stay on, how long they run, and how to size a system for your home.
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What happens the moment
the grid goes down.
The battery detects the outage in milliseconds.
Both Powerwall 3 and Enphase IQ Battery 5P monitor grid frequency continuously. When grid power drops, the battery islands your home from the grid and switches to backup mode automatically. The transition happens faster than a generator startup and faster than most appliances notice.
Backed-up circuits stay live. Non-backed circuits go dark.
Your home battery powers only the circuits that were connected to the backup panel during installation. Typically this is your critical loads: refrigerator, lights, select outlets, internet router, phone chargers, medical equipment. Circuits that are not on the backup panel go dark when the grid fails.
If you have solar, the battery recharges during daylight.
During a daytime outage, your solar panels continue to produce power. That production charges the battery instead of exporting to the grid. A well-sized solar plus battery system can sustain critical loads through a multi-day outage, recharging each day as the sun comes up.
When grid power returns, the battery reconnects automatically.
When PG&E or SMUD restores grid power, the battery detects the stable grid signal and reconnects automatically. No manual switching. You get a notification in the Tesla app or Enphase Enlighten app confirming the transition.
Typical loads and how much
power they draw.
The amount you can run at once depends on your battery's continuous power output. A Powerwall 3 outputs 11.5 kW. An Enphase IQ Battery 5P outputs 3.84 kW per unit. Here's where common appliances land.
Low draw — runs easily on any battery
High draw — depends on battery capacity and output
Most homeowners run the first column all the time during an outage and selectively run items from the second column. A Powerwall 3 at 11.5 kW continuous can handle central AC plus the essential loads simultaneously. An Enphase 5P at 3.84 kW per unit needs multiple units to run central AC alongside other loads.
How long one Powerwall 3
lasts during an outage.
Starting from a full 13.5 kWh charge. What you run determines how long it lasts. These are estimates.
All estimates based on a single fully charged Tesla Powerwall 3 (13.5 kWh). Two units doubles duration. Enphase IQ Battery 5P at 5 kWh per unit scales proportionally. Actual results depend on temperature, actual load, solar conditions, and starting charge level.
PSPS outages in the foothills
last days, not hours.
PG&E's Public Safety Power Shutoffs cut power proactively when high winds and dry conditions create fire risk. These events primarily affect foothill communities: Auburn, Rocklin, Granite Bay, El Dorado Hills, and surrounding areas.
PSPS events typically last 12 hours to 5 days depending on weather. A battery without solar can cover one night. A battery with solar can cover a multi-day event by recharging each day as the sun comes up.
For homeowners in high PSPS frequency zones, the backup case for solar plus battery is as strong as the financial case. The two work together.
Whole-home backup vs
critical load backup.
Critical load backup
A subpanel with selected circuits: refrigerator, lighting zones, outlets, router, phone charging, medical equipment. Most of the home feels normal during an outage. Only high-draw appliances like central AC or the electric range are excluded.
Whole-home backup
The battery backs up the entire main panel. Every circuit in the home works as normal during an outage, including central AC, the oven, and the EV charger. Requires more battery capacity and a higher-output system.
We ask you upfront what matters most during an outage. Most homeowners we talk to want critical load backup: keep the food cold, keep the lights on, keep the phones charged. That's well within a single Powerwall 3 or a two-unit Enphase stack. If you need AC too, we size accordingly.
Also worth reading.
Home Battery
Full service page. SMUD rebate up to $10,000, install timeline, what's included.
See the service →Powerwall vs Enphase
Which battery handles higher backup loads. Side by side on power output and capacity.
Compare →SMUD Rebate
Up to $10,000 per home for Sacramento area homeowners. First come, first served.
Full details →NEM 3.0
Why a battery is the fix for PG&E solar economics in 2026. Export credits down 75%.
Read the explainer →Battery backup questions
we hear every week.
How long does a home battery last during a power outage?
It depends on what you run and how much capacity you have. A single Powerwall 3 (13.5 kWh) running essentials only, refrigerator, lights, router, and phone charging, typically lasts 17 to 27 hours. Add a mini-split AC and you're looking at 5 to 9 hours. Add central AC and it drops to 2 to 4 hours. If you have solar and the outage happens during daylight, the battery recharges from your panels and extends backup significantly.
What is a PG&E PSPS event?
PSPS stands for Public Safety Power Shutoff. PG&E proactively cuts power to high-fire-risk areas when weather conditions create wildfire danger, typically high winds combined with low humidity. These events primarily affect foothill communities including Auburn, Rocklin, Granite Bay, and El Dorado Hills. Shutoffs can last 12 hours to 5 days. A home battery with solar recharges during daylight and can sustain critical loads through a multi-day event.
Does my home battery switch on automatically during an outage?
Yes. Both Powerwall 3 and Enphase IQ Battery 5P switch to backup mode automatically within milliseconds of detecting a grid outage. You may notice a brief flicker and then your backed-up circuits are live. Appliances do not need to be manually switched. The transition is significantly faster than a generator startup.
Can I run air conditioning on a home battery?
It depends on the battery. A Powerwall 3 outputs 11.5 kW continuous, which is enough to run a central AC system along with other loads. An Enphase IQ Battery 5P outputs 3.84 kW per unit, which may not handle a large central AC compressor on its own. Multiple Enphase units solve this. A mini-split AC runs more efficiently than central AC during backup. We size your backup load at the consult so you know exactly what runs.
Does battery backup require solar?
No. A standalone battery provides outage backup from stored grid energy without solar. During a daytime outage with solar, the battery recharges from your panels and extends backup duration. Without solar, you start with whatever charge is in the battery when the outage begins. For multi-day PSPS events, solar plus battery is significantly more resilient than battery alone. A standalone battery in SMUD territory still qualifies for the rebate up to $10,000.
Size a backup system
for your home.
We look at your loads, your usage, your utility, and your roof. We design backup that actually covers what you need. No pressure. No same day close.