The lights in your street are out, and it’s the first indication that your area is experiencing a blackout. This is the reality of a home with blackout protection – oftentimes, you’ll never even know. Home battery storage offers homes the ability to function when the grid goes down, but have you considered how long this can be sustained? Many factors affect your battery’s ability to power your home, including capacity, inverter size, whether your home is set up for partial or whole-home backup, and what you’re powering.
Battery runtime by capacity and usage
Understanding how long a battery will last during a blackout starts with capacity and consumption. The table below provides a practical snapshot of how different battery sizes perform under average and high household usage. It also compares how long each system may last when running essential circuits only, versus powering the entire home.
| Battery size (kWh) | Avg household use (kWh/day) | High use (air con, pool, etc) (kWh/day) | Partial backup runtime | Whole home runtime |
| 5 | 10–15 | 20–30 | 8–12 hours | 3–6 hours |
| 10 | 10–15 | 20–30 | 16–24 hours | 6–10 hours |
| 15 | 12–18 | 25–35 | 1–2 days | 10–16 hours |
| 20 | 12–20 | 25–40 | 1.5–2.5 days | 12–20 hours |
| 25 | 15–22 | 30–45 | 2–3 days | 16–24 hours |
| 30 | 15–25 | 35–50 | 2.5–3.5 days | 18–30 hours |
| 35 | 18–28 | 40–55 | 3–4 days | 24–36 hours |
| 40 | 18–30 | 45–60 | 3.5–5 days | 30–40 hours |
| 45 | 20–32 | 50–65 | 4–5.5 days | 36–48 hours |
| 50 | 20–35 | 55–70 | 4.5–6 days | 40–60 hours |
These figures are indicative, but they highlight a key point. Your battery life during a blackout depends less on size alone and more on how you use your energy.
Partial vs whole home backup explained
One of the biggest factors affecting blackout performance is whether your system is set up for partial or whole-home backup.
Partial backup means only essential circuits are powered, such as:
- Fridge and freezer
- Lights
- Internet and devices
- A few power points
Whole home backup means everything is live, including:
- Air conditioning
- Pool pumps
- Electric hot water systems
- Kitchen appliances
Here is the reality. Partial backup dramatically extends battery life. Whole-home backup gives convenience, but burns through stored energy far faster.
If you are aiming for resilience, partial backup is often the smarter choice. If you want full comfort, you will need a larger battery to support it.
Real-world example: a 48 kWh battery in action
Let’s bring this into the real world.
My home is backed up by a 48 kWh GoodWe ESA All-in-One with whole-home backup. Under normal conditions, we do not rely on the grid overnight. Instead, we take advantage of GloBird’s three hours of free electricity, then discharge through the evening to maximise savings with the VPP.
On a typical day:
- Our battery drops to around 30% overnight
- This means that we use roughly 70% or 33.6 kWh, but this includes discharging to the grid
- Actual home usage is generally 24 kWh, so 50% of our battery’s capacity
Now consider blackout conditions. There is:
- No free grid charging
- No discharging
- Full reliance on stored energy and solar
On a good summer day:
- Solar generation fully recharges the battery
- We can effectively run our home indefinitely
- This assumes sensible usage
On a cloudy or poor generation day:
- The battery may only recharge to 50 to 70%
- Our available energy shrinks quickly
- We need to actively manage usage
This is where behaviour becomes just as important as hardware.
Read more about my GoodWe ESA All-in-One installation.
How solar extends blackout runtime
Solar is the wildcard that changes everything. Without solar, your battery is a fixed bucket of energy. Once it is empty, you are done.
With solar:
- Your system can recharge during daylight hours
- You can extend the runtime across multiple days
- You can potentially operate indefinitely
However, there are limits:
- Winter sunlight hours are shorter
- Cloud cover reduces output
- Panel orientation and system size matter
This means that during winter blackouts, even large batteries require careful energy management.
What drains your battery the fastest
If you want your battery to last, you need to understand your biggest energy users.
The main culprits are:
- Air conditioners
- Pool pumps
- Electric ovens and cooktops
- Dishwashers and washing machines
- Electric hot water systems
These appliances can quickly chew through your stored energy.
For example:
- A ducted air conditioner can draw 3 to 6 kW per hour
- A pool pump can run for hours at a time
- Heating water electrically can spike consumption
During a blackout, these loads can halve your runtime.
How to make your battery last longer
If you want to ride out a blackout comfortably, a few simple strategies go a long way.
Prioritise essential loads:
- Keep fridges, lighting, and communications running
- Switch off non-essential circuits or simply at the power point
Reduce peak demand:
- Avoid running multiple large appliances at once
- Delay washing and dishwashing
Be strategic with air con:
- Use it sparingly
- Focus on heating or cooling one room
Monitor your system:
- Use your app to track battery levels
- Adjust behaviour in real time
Leverage solar wisely:
- Run heavier loads during daylight hours
- Let solar do the heavy lifting
This approach can stretch your battery from hours into days.
Choosing the right battery size for blackout protection
If blackout protection is a priority, sizing matters.
Here is a simple way to think about it:
| Goal | Recommended battery size |
| Basic backup (essentials only) | 10–15 kWh |
| Comfortable partial backup | 15–25 kWh |
| Whole home backup (short duration) | 20–35 kWh |
| Whole home backup (extended) | 35–50 kWh |
A larger battery gives you flexibility, but only if you manage your loads.
Riding a blackout with a battery: it is about control, not just capacity
A home battery does not just provide backup. It gives you control.
During a blackout:
- Partial backup gives you endurance
- Whole home backup gives you convenience
- Solar gives you longevity
In my case, a 48 kWh system paired with solar is a powerful setup. With smart usage, we can comfortably weather multi-day outages.
So, how long will a home battery last in a blackout? The honest answer is that it depends, but you can expect anywhere from a few hours to several days. Smaller systems running a full home may only last half a day, while larger batteries with partial backup can stretch across multiple days. Add solar into the mix, and you can potentially keep your home running indefinitely, provided there is enough sunlight, and you manage your usage. In the end, battery capacity sets the ceiling, but your habits determine how long you actually stay powered when the grid goes down.
Power your home throughout the night and during blackouts with home energy storage. Request FREE and no-obligation quotes today.
