Battery Backup for Power Outages — What Can You Run?

Quick Answer

A properly installed home battery can usually run essential loads such as a refrigerator, LED lights, Wi-Fi router, phone charging, security system, laptop, medical device charging and a few general outlets. These loads are often small enough that a 5kWh to 10kWh battery can keep them running for many hours, especially if solar recharges the battery during the day.

Large appliances are different. Air conditioners, electric ovens, kettles, toasters, induction cooktops, pool pumps, bore pumps, welders, EV chargers and electric water heaters can use a lot of power. Some may exceed the inverter’s backup output, trigger overload protection or drain the battery very quickly. A 10kWh battery sounds large, but a 3kW load can drain it in only a few hours after losses and reserve are considered.

The best backup design is usually selected essential circuits, not “run everything as normal.” A fridge, lights, internet and a few outlets can keep a household comfortable for a long outage. Whole-home backup is possible with some systems, but it needs more battery capacity, stronger inverter output, careful wiring and disciplined load management.

Capacity vs Power: The Most Common Confusion

Battery capacity is measured in kWh. It tells you how much energy is stored. Inverter output is measured in kW. It tells you how much power the system can deliver at one moment. A 10kWh battery with a 5kW backup inverter can run up to 5kW of load for a limited time, but it cannot run 10kW of appliances just because the battery has 10kWh of energy.

Think of capacity like the size of a water tank and inverter output like the size of the pipe. A large tank with a small pipe cannot deliver a huge flow at once. A large pipe with a small tank can deliver high power but run out quickly. A good backup system needs both enough stored energy and enough output power for the appliances you expect to run.

Surge power also matters. Motors in fridges, pumps and air conditioners can draw a brief starting surge higher than their running power. Some inverters can handle this; others may trip. Always check both continuous output and surge rating before backing up motor loads.

Essential Loads vs Whole-Home Backup

Essential-load backup means only selected circuits are connected to the backup output. This might include the fridge, lights, Wi-Fi, security system, garage door, medical device charging and a few outlets. It keeps the battery focused on what matters most and avoids accidental overload from heavy appliances.

Whole-home backup connects most or all circuits behind backup hardware. It can feel more convenient because you do not need to think as much during an outage. However, it also increases the risk that someone turns on a kettle, oven, heater or air conditioner and drains the battery quickly. Whole-home backup needs a bigger inverter, more battery capacity, transfer equipment and clear household rules.

For most households, essential-load backup is the smarter first design. It costs less, lasts longer and is easier to control. Whole-home backup is best for homes that have the budget, electrical design and battery size to support it properly.

Appliance Guide: What Usually Works

Fridge and freezer: usually realistic. They cycle on and off, so average power is much lower than peak power. Keep doors closed to reduce runtime loss.

LED lighting: very easy. A few LED lights may use less power than one older incandescent bulb. Lighting is one of the best backup loads.

Wi-Fi, phones and laptops: easy and highly valuable. Internet and communications use little energy compared with comfort appliances.

Water pumps: possible but must be checked. Pumps can have high starting surge, so inverter surge rating and pump size matter.

Air conditioning: possible with efficient split systems and enough inverter capacity, but it can reduce runtime dramatically. Large ducted systems are much harder.

Cooking appliances: use carefully. Kettles, ovens and induction cooktops draw high power. A small microwave used briefly may be more practical than full electric cooking during a long outage.

Solar During a Blackout

Many people assume rooftop solar automatically works during a blackout. Standard grid-tied solar usually shuts down when the grid fails. This is a safety feature that prevents solar from feeding a dead grid while utility workers may be repairing lines. To keep solar running during an outage, the home needs a backup-capable hybrid inverter, battery and correct islanding/backup hardware.

When properly designed, solar can recharge the battery during the day and make a smaller battery feel much larger. For example, a 10kWh battery may cover night-time essentials, then solar can refill it the next day. During cloudy weather, smoke, storms or short winter days, solar recharge may be limited, so backup planning should not rely on perfect sunshine.

Ask your installer whether your system can form a backup microgrid, whether solar will continue operating during outages, whether there is a minimum battery reserve required for solar restart, and what happens if the battery is completely flat when the sun comes out.

Battery Size Examples for Outages

5kWh battery: good for essential loads, short outages and small homes. It can often run fridge, lights and Wi-Fi overnight if heavy loads are avoided. It is not ideal for long outages with air conditioning or pumps.

10kWh battery: a strong middle option. It can cover essential loads for many hours and may support a small split AC for limited periods. It is often enough for overnight resilience when solar can recharge the next day.

13.5kWh to 15kWh battery: better for larger homes, longer outages, moderate comfort loads and stronger backup plans. It can still be drained quickly by cooking, heating, EV charging or large air conditioning.

20kWh+ battery: useful for backup-first homes, rural properties, pumps, longer outages or high-consumption households. Cost, inverter output and wiring complexity increase, so the design should be justified by real needs.

Medical, Safety and Critical Loads

If someone in the home relies on medical equipment, backup design needs extra care. Do not rely only on a general battery sizing estimate. Confirm the medical device power requirement, runtime need, backup circuit location, transfer time and whether the device can tolerate brief interruptions. Keep manufacturer guidance and emergency plans available.

Security systems, gates, garage doors and communication equipment can also matter during outages. These loads are usually small, but they should be included in the backup circuit list. If the property has electric gates, sump pumps, pressure pumps or water tanks, ask the installer about surge current and whether manual backup options are needed.

Battery backup can improve resilience, but it should not be the only emergency plan. For long outages, keep torches, power banks, drinking water, non-electric cooking options where safe, and a clear household load-shedding plan.

Common Mistakes to Avoid

• Assuming battery size equals power: kWh is stored energy; kW is instant output.
• Backing up too many circuits: heavy loads can drain the battery or trip the inverter.
• Forgetting starting surge: pumps, fridges and air conditioners may need more power when starting.
• Assuming solar always works: grid-tied solar needs backup-capable equipment to operate during outages.
• Ignoring reserve settings: some systems keep a backup reserve, reducing everyday usable capacity.
• Not testing backup: simulate an outage after installation so you know which circuits work.

Quote Checklist Before Buying

A backup battery quote should clearly explain usable capacity, continuous backup output, surge output, backed-up circuits, transfer equipment, solar recharge during outage, reserve settings, warranty terms and any switchboard upgrades. If the quote only says “whole home backup,” ask exactly what that means and which loads are excluded.

Ask the installer to show a backup load list. The list should separate essential loads from optional loads and heavy loads. It should also show whether air conditioning, pumps, electric cooking, hot water or EV charging are included or blocked during outage operation. A clear list prevents disappointment when the first blackout happens.

5kWh, 10kWh and 15kWh Backup Scenarios

5kWh scenario: best for a simple outage plan. Keep the fridge, freezer, Wi-Fi, modem, a few LED lights, phone charging and one or two low-power outlets running. Avoid air conditioning, kettles, ovens, pumps and electric heaters. This size can be excellent for short outages if the household understands the limits.

10kWh scenario: the practical middle ground. It can run essential loads overnight and may support small comfort loads such as fans, laptops or a small efficient split system for limited periods. With daytime solar recharge, a 10kWh battery can feel much larger during multi-day outages, but cloudy weather should still be planned for.

15kWh scenario: better for homes that want longer runtime, more comfort loads or stronger backup reserve. It can support essentials plus moderate extra use, but it still cannot run every heavy appliance without planning. If someone turns on cooking loads, pumps and air conditioning together, even a large battery can drain fast or overload.

Load-Shedding Rules for Long Outages

During a short outage, you may not need strict rules. During a long outage, load control matters. Turn off non-essential lights, avoid electric cooking, delay laundry, avoid pool pumps, limit air conditioning, and keep fridge and freezer doors closed. Use battery monitoring to watch state of charge and reduce loads before the battery becomes critically low.

A useful rule is to split loads into three groups: must-run, comfort and avoid. Must-run loads include fridge, medical needs, Wi-Fi, security and basic lights. Comfort loads include fans, laptops and a small AC used carefully. Avoid loads include EV charging, electric hot water, ovens, kettles and large heating unless the system was designed for them.

Testing Your Backup System

After installation, ask the installer to perform a controlled backup test. The test should show which circuits stay on, whether solar continues operating, whether the battery charges during islanded operation, and what happens when a heavier load is switched on. Do not wait for a real outage to discover that the wrong circuit was backed up.

Keep a simple backup map near the switchboard or in your home energy folder. It should list backed-up circuits, appliances to avoid, battery reserve settings, installer contact details and the steps to check the monitoring app. This is especially helpful for family members who were not present during installation.

Final Recommendation

For most homes, the best battery backup design is a selected essential-loads system. It keeps the fridge cold, lights on, internet working and phones charged while preserving battery runtime. A 5kWh battery can cover short essential outages, a 10kWh battery is a balanced option, and 13.5kWh to 15kWh batteries suit larger homes or longer backup needs.

Whole-home backup can be excellent, but only when the battery, inverter, wiring and load rules are designed properly. Before buying, ask what the battery can run, how long it can run, whether solar works in a blackout and what appliances must stay off. The right backup system is the one that keeps essential life running without pretending every appliance can operate as normal.