It depends on two numbers and one wiring decision, and most people find that out after the grid goes down rather than before. A home battery does not automatically keep your whole house running through an outage. What it powers is set by the inverter’s continuous power output, the energy stored in the battery, and which circuits your installer connected to backup in the first place.
Get those three right and a blackout becomes a non-event you notice only through the monitoring app. Get them wrong and you own an expensive battery that switches off at the exact moment you wanted it most.
A correctly configured home battery can typically run low and medium draw loads through a blackout: lights, the fridge, internet, phone and laptop charging, the television, and general power points. High-surge, high-draw appliances such as ducted air conditioning, electric ovens, instantaneous hot water and EV charging usually need a larger, more powerful system and often sit outside backup by design.
Two things decide the outcome. Stored energy, measured in kilowatt-hours, sets how long backup lasts. Continuous power output, measured in kilowatts, sets what can run at any one moment. A large battery with a modest inverter can hold plenty of energy yet still trip if you switch on too much at once.
First, a Catch Most People Miss
By default, a grid-connected battery shuts down the instant the grid fails. This is a safety requirement, not a fault. It stops your system feeding electricity into network lines that repair crews may be working on.
To keep power flowing during an outage, the system has to isolate your home from the grid and form its own self-contained circuit, a process called islanding. That switchover usually happens automatically in a fraction of a second, sometimes fast enough that you only notice a brief flicker. But it only happens if the system was specified with backup capability in the first place.
This is the single most important sentence in the article: a battery bought purely to cut your bills may have no blackout function at all. If backup matters to you, it has to be designed in, and you have to ask for it explicitly before installation. Retrofitting it afterwards costs more than building it in. The broader pros and cons of battery ownership cover where backup sits among the other reasons people buy.
Do You Actually Need Backup Power?
Not every household does, and backup capability adds cost, so it is worth deciding deliberately rather than by default. Ask yourself:
- Is your area prone to storms, bushfires or extended outages? Sydney’s outer suburbs, the Blue Mountains and regional NSW see this more than the inner city.
- Are there specific things you need running through an outage, such as the fridge, internet or lights?
- Does anyone in the home rely on powered medical equipment?
- How long do outages in your area typically last, minutes or hours?
If outages are rare and brief where you live, a battery configured purely for bill savings may be all you need, and you can put the money you would have spent on backup hardware toward more storage instead. If outages are frequent, long, or you have a genuine need to keep specific things running, backup earns its place. There is no universal answer, only the one that fits your street and your household.
A VPP Battery Is Not Automatically a Backup Battery
Worth clearing up, because it catches people out. A battery set up to earn income through a Virtual Power Plant is designed for that purpose, trading energy with the grid, not necessarily for keeping your home running in an outage. The two functions can coexist, but one does not guarantee the other.
If you are joining a VPP and you also want blackout protection, treat them as two separate requirements and confirm both are specified. Do not assume that because your battery talks to the grid for market participation, it will island and power your home when the grid drops.
The Two Numbers That Decide Everything
Stored energy (kWh) sets duration. If your battery holds 10 kilowatt-hours of usable energy and your backed-up loads draw 1 kilowatt on average, you have roughly ten hours before it empties, less once efficiency losses are counted. Draw less and it lasts longer.
Continuous power output (kW) sets the ceiling. Home battery inverters commonly deliver somewhere in the range of about 3.3 to 5 kilowatts of continuous output. Everything running at once has to fit under that ceiling. Exceed it and the system protects itself by shutting down, regardless of how much energy is still in the battery.
The distinction trips people up because the marketing headline is almost always the kilowatt-hour figure. A 15 kilowatt-hour battery sounds like it should run anything. It will not, if its inverter caps output at 5 kilowatts and you try to start a ducted air conditioner.
Surge Power: The Hidden Third Number
Some appliances draw far more power to start than to run. Anything with a motor or compressor, fridges, pool pumps, air conditioners, does this. The brief spike when the motor kicks in is called surge or startup power, and it can be several times the appliance’s running draw.
A fridge that runs on a few hundred watts might demand a couple of thousand watts for the split second its compressor starts. Your system needs enough surge headroom above its continuous rating to absorb that spike, or the appliance simply will not start on backup even though it runs fine on the grid.
This is why “will it run my air conditioner in a blackout” rarely has a simple yes. The answer depends on the air conditioner’s starting surge, the inverter’s surge capability, and what else is drawing power at the same moment.
Whole-Home Backup vs Essential Circuits
There are two ways to wire backup, and the choice shapes both cost and how long your battery lasts in an outage.
Essential circuits backup. Selected circuits, typically lights, the fridge, power points and internet, are wired to a dedicated backup sub-board. When the grid fails, only those circuits stay live. Because the backed-up load is small, the battery lasts far longer, and the hardware and wiring cost less. This is the most common and most practical choice for the majority of homes.
Whole-home backup. Every circuit in the house can stay energised during an outage, air conditioning and all, subject to the battery’s capacity and the inverter’s output ceiling. It needs a larger, more powerful system, a backup gateway, and more extensive wiring, so it costs more. It suits homes with medical equipment, frequent extended outages, or a strong preference for the house behaving normally through a blackout.
Neither is inherently better. Essential circuits gives you longer runtime on the things that matter for less money. Whole-home gives you normality at a higher price and shorter runtime under heavy load. The right answer comes from listing what you actually need running before you buy, not after.
What Typically Stays On, and What Usually Doesn’t
Treat this as a general guide, not a specification. Your actual result depends on your system’s output, its stored energy and how it was wired.
| Usually manageable on backup | Often excluded or needs a larger system |
| LED lighting | Ducted or multiple air conditioners |
| Refrigerator and freezer | Electric oven and cooktop |
| Internet modem and Wi-Fi | Instantaneous electric hot water |
| Phone and laptop charging | EV charging |
| Television and small electronics | Pool and spa pumps |
| Power points for small appliances | Electric heating across the whole home |
| A single split-system air conditioner, if sized for it | Workshop and three-phase equipment |
The pattern is straightforward: low and steady loads are easy, high-draw and high-surge loads are hard. A system can be designed to handle the harder loads, but that is a deliberate sizing decision with a cost attached, not something any battery does by default.
How Long Will It Last?
Runtime is stored energy divided by the load you are running, adjusted down for losses. The variable people forget is that the load is not fixed. Running only the fridge, a few lights and the modem might draw a couple of hundred watts, stretching a mid-sized battery across a night or more. Add a heater or air conditioner and the same battery could empty in a couple of hours.
Solar changes the picture in daylight. If your system is configured so the panels keep generating during an outage, they can recharge the battery through the day, extending backup well beyond what the battery alone would give, potentially indefinitely in good weather across a prolonged outage. This depends on the system supporting solar charging while islanded, which is worth confirming rather than assuming.
Sizing for backup is a different calculation from sizing for bill savings, because you are planning around a worst-case evening rather than an average day. Our guide to choosing a battery size for your home covers the method, and it is worth telling your installer explicitly if backup runtime is a priority.
Making Backup Last Through a Long Outage
If an outage stretches into a second day, a few habits extend your reserves considerably:
- Switch non-essential appliances off at the wall, not just standby, so they stop quietly drawing power.
- Keep the fridge and freezer closed as much as possible, since they hold their temperature for hours when left shut.
- Run heavy loads, if you must run them at all, during daylight when solar is topping the battery up rather than after dark.
- Use your monitoring app to see what is drawing power and where you can cut back, so you are managing reserves on data rather than guesswork.
The goal is simple: match your consumption to what the battery and any daytime solar can sustain, so you are not caught with an empty battery at nightfall.
If Someone Relies on Medical Equipment
This deserves its own treatment, because the stakes are different. If anyone in the household depends on powered medical equipment, a CPAP machine, oxygen concentrator, or anything life-sustaining, backup is not a convenience feature, it is a safety requirement, and the system has to be sized for that specific device’s continuous draw plus everything else running alongside it.
Two points matter here. First, a home battery should be treated as one layer of resilience, not a guaranteed sole power source for life-critical equipment, because any system can fail or be depleted. Government guidance is explicit that home battery systems are typically not appropriate as the primary power source for life-support loads. Independent backup arrangements and a plan for extended outages remain essential. Second, households with life-support equipment can usually register with their electricity retailer or network for life-support protections. That registration is a separate process from installing a battery and does not depend on having one. Speak to your retailer about it directly, and seek specialist advice on backup for the specific equipment involved.
If this applies to you, say so clearly at the assessment stage so the system can be designed around the requirement rather than sized for general convenience.
Safety and Standards
Backup wiring is regulated work. Battery installations must comply with AS/NZS 5139:2019, and backup configurations bring additional wiring and switchboard requirements on top of a standard install. Whole-home backup in particular can require specific protective devices on circuits, which is one reason it costs more and why it must be designed and certified by an appropriately accredited installer.
The practical implication is that backup is not a setting toggled on at the end. It is a design decision that affects the switchboard, the protective devices and the wiring, and it needs to be scoped at quote stage. Any quote promising blackout capability without a site inspection is describing an aspiration, not a design.
Battery installers must hold Solar Accreditation Australia battery endorsement specifically, and installations are subject to sample inspection by the Clean Energy Regulator with the homeowner’s consent. Checking your installer’s accreditation takes two minutes and is worth doing.
Backup Configurations Compared
| Essential circuits backup | Whole-home backup | |
| What stays on | Selected circuits only | Every circuit, subject to capacity and output |
| Runtime under load | Longer, smaller load | Shorter when heavy loads run |
| System size needed | Smaller battery and inverter | Larger battery, higher output inverter |
| Extra hardware | Backup sub-board | Backup gateway and broader wiring |
| Typical cost position | Lower | Higher |
| Best suited to | Most homes, occasional outages | Medical needs, frequent long outages, whole-house preference |
| Handles air conditioning | Usually no, or one small unit | Possibly, if sized for it |
How to Get the Backup You Actually Want
The gap between what people expect and what they get almost always comes from skipping this conversation before purchase. Work through it before you sign:
- List the specific appliances you need running in an outage, including any medical equipment.
- Note which of them have motors or compressors, since those carry surge demands.
- Decide honestly between essential circuits and whole-home, based on that list and your budget.
- Ask for the inverter’s continuous power output and surge capability in writing.
- Ask for the usable stored energy, not just the nominal figure.
- Confirm whether solar can recharge the battery during a grid outage.
- Confirm the backup switchover is automatic and how the specific circuits will be wired.
- Get it all scoped from a physical site inspection, not an estimate.
The Practical Position
A home battery can power a genuinely useful slice of your home through a blackout, comfortably the fridge, lights, internet and device charging on a well-configured system, and considerably more if you size and wire it for that. What it cannot do is read your mind. The battery that keeps your whole house running through a summer outage and the battery that quietly saves you money on bills are often different specifications, even from the same product range.
The deciding factors are within your control, but only before installation: the coupling and gateway hardware, the inverter’s output, the stored capacity, and the choice between essential circuits and whole-home backup.
Greenlight Solar can assess what you need running in an outage, work out the continuous output and capacity required, and design backup wiring to match rather than leaving it to chance. Request a site assessment to find out what backup would look like for your home.
Frequently Asked Questions
Will a solar battery work during a blackout?
Only if it was set up for it. A standard grid-connected battery shuts down when the grid fails, for safety. Backup power requires a battery and inverter capable of islanding, plus backup wiring, and this has to be specified before installation rather than added as an afterthought.
What can a home battery run in a power outage?
Typically lights, the fridge and freezer, internet, device charging, the television and general power points. High-draw appliances like ducted air conditioning, electric ovens, EV charging and pool pumps usually need a larger, higher-output system and are often left off backup to preserve runtime.
Can a home battery run air conditioning in a blackout?
Sometimes, but not by default. Air conditioners draw a large surge of power to start, so the system needs enough continuous output and surge headroom to handle it. A single split-system can often be backed up if the system is sized for it. Ducted units usually need a larger, purpose-designed setup.
How long will a home battery last in a blackout?
It depends on how much you are running. A battery powering only essentials like the fridge, lights and modem may last through a night or longer, while running heaters or air conditioning could empty it in a couple of hours. If solar can recharge the battery during daylight, backup can extend much further.
Do I need a special inverter or gateway for blackout backup?
Yes. Backup needs an inverter capable of islanding, and whole-home backup usually needs a dedicated backup gateway plus additional wiring. A battery configured only for bill savings may have none of this, which is why backup capability must be requested and designed in from the start.
What is the difference between whole-home and essential-circuit backup?
Essential-circuit backup powers selected circuits such as lights, fridge and power points through a dedicated sub-board, lasts longer and costs less. Whole-home backup can power every circuit but needs a larger, more powerful system and costs more. Most homes are well served by essential-circuit backup.
Does a battery connected to a VPP still work in a blackout?
Not automatically. A battery set up for Virtual Power Plant participation is designed to trade energy with the grid, which is a different function from backup. If you want both, confirm that blackout capability is specified separately, rather than assuming VPP capability includes it.
Can I run medical equipment on a home battery during an outage?
A battery can help, but it should not be your only safeguard for life-critical equipment, and government guidance advises it is typically not suitable as the primary power source. Size the system for the device’s continuous draw, seek specialist advice, and register for life-support protections with your retailer or network, which is a separate process from installing a battery.
