Battery Backup for Load Shedding: Sizing Your System

By Hermes

Last updated: September 21, 2026

With ongoing load shedding in South Africa, battery backup systems have become essential for homes and businesses. Properly sizing your battery system ensures you have enough power when you need it most.

How to Calculate Battery Runtime

Battery runtime depends on battery capacity (kWh), inverter efficiency, and your load (watts). Use our Battery Runtime Calculator to determine how long your battery will last during load shedding.

Inverter Sizing

Your inverter must handle the maximum load you plan to run during outages. Use our Inverter Calculator to find the right size.

Common Misconceptions About Battery Backup Systems

When load shedding became a regular part of life in South Africa, many households rushed to buy battery backup systems without fully understanding them. A common misconception is that a battery backup system will power your entire home. In reality, most residential systems are designed to keep essential appliances running, such as lights, a router, and a television, for a limited time. Running high-draw appliances like a geyser, an oven, or an air conditioner requires a much larger and more expensive system.

Another misconception is that the size of the battery is the only thing that matters. The inverter’s capacity, the type of battery, and the way the system is wired all affect how much you can run and for how long. There is also a belief that a backup system will pay for itself quickly through savings. While it can protect you from the inconvenience of load shedding, it does not reduce your electricity bill unless it is paired with solar panels. Understanding what a system can and cannot do helps you choose the right solution for your needs and budget.

Why Battery Backup Became Essential

The years of widespread load shedding transformed how South African households and businesses think about their electricity supply. When the power went out for hours at a time, the inability to keep fridges running, internet connected, and lights on was more than an inconvenience — it threatened food safety, work productivity, communication and even security. This drove a boom in battery backup systems, which allow homes and businesses to keep essential appliances running during outages. Understanding how these systems work, what they cost and what they can and cannot do is essential for anyone considering one.

A battery backup system stores electrical energy that can be drawn upon when the grid fails. The most common configuration consists of an inverter, a battery bank, and a connection that allows the system to charge from the grid when power is available and to supply stored power when it is not. When load shedding begins, the system automatically switches over and keeps the connected appliances running for as long as the battery capacity lasts. The size of the system determines how much power it can supply and for how long, and matching that to your needs is the key to a good investment.

Understanding Inverters and Battery Capacity

The two central components of a battery backup system are the inverter and the battery. The inverter converts the direct current (DC) stored in the battery into the alternating current (AC) that your appliances use. Its power rating, measured in kilowatts (kW), determines how much electrical load the system can supply at any one time. If you want to run a fridge, lights, a TV and a router, you need an inverter with a sufficient power rating to handle their combined load. Choosing an inverter too small for your needs will result in it tripping or shutting down under load.

The battery determines how long your system can supply power. Battery capacity is measured in kilowatt-hours (kWh), which indicates how much energy the battery can store. A 5kWh battery can supply 5kW of power for one hour, or 1kW for five hours. In South Africa, where load shedding can last for several hours, most households choose a battery with enough capacity to power their essential appliances for the duration of a typical outage. Advances in lithium-ion technology have made batteries more powerful, more compact and more affordable, and they are now the standard choice for most installations.

Costs, Payback and Choosing the Right Size

The cost of a battery backup system in South Africa varies widely depending on its size and quality. A small system designed to keep the lights, router and a fridge running during outages might start at around R20,000 to R40,000. A larger system capable of powering most of a home for several hours could cost R60,000 to R150,000 or more. These costs have fallen significantly in recent years as technology has improved and more suppliers have entered the market, but they remain a significant investment for most households, so it is important to choose the right size for your needs.
A battery is only half the job if the router and ONT are not on it, and this walkthrough of the fibre ONT, router and switch explains what has to stay powered.

The right size depends on what you actually need to keep running during an outage. Start by identifying your essential loads — the appliances you genuinely cannot do without — and their total power consumption. This tells you the inverter size and battery capacity you need. It is usually more cost-effective to buy a system sized for your essentials rather than trying to power everything in your home, which would require a much larger and more expensive installation. A reputable installer can help you assess your needs and design a system that provides reliable backup without unnecessary expense.

Solar-Plus-Battery: The Complete Solution

For many South Africans, the ultimate solution to both load shedding and high electricity bills is a solar-plus-battery system. This combines solar panels with an inverter and battery storage, allowing you to generate your own electricity during the day, store excess in the battery, and use that stored energy at night or during outages. The solar panels reduce your reliance on the grid and can significantly lower your monthly electricity bill, while the battery provides backup power when the grid fails. Together, they offer both independence and savings.

A solar-plus-battery system is a larger investment, but it addresses both the reliability problem and the cost problem. During daylight hours, the panels generate electricity that powers your home and charges the battery; any surplus can, in some areas, be fed back to the grid for a credit. At night, the battery supplies the stored power, reducing what you draw from the grid. Over time, the savings on your electricity bill can help offset the cost of the system. As load shedding becomes less frequent but electricity prices continue to rise, solar-plus-battery has become an increasingly attractive option for South African households and businesses alike.

Choosing the Right Backup Power System for Your Home

When you compare backup power options, think about what you are actually trying to keep running during load shedding. A simple inverter with a battery will keep lights, a Wi-Fi router, and a laptop going for several hours, which is enough for most households to stay productive and connected. A larger system with more battery capacity can also run a fridge or a television, while a generator is the only practical way to keep power-hungry appliances like a geyser, stove, or air conditioner running.

Work out your power needs in watts before you buy. Add up the wattage of the devices you want to run simultaneously, then choose an inverter and battery that can handle that load plus a margin for safety. A common mistake is buying an inverter that is too small for the appliances you intend to power, which causes the system to trip or the battery to drain quickly. It is also worth checking how long the battery will last on a single charge, because this varies widely depending on the size of the battery and the load you put on it.

Think about the future as well. If you plan to add a solar panel later to charge the battery during the day, choose a system that supports that upgrade rather than one you will have to replace. Many reputable South African suppliers offer battery backup packages that are sized for typical household use, and it is worth getting advice based on your specific situation before spending money on a system that does not meet your needs.

Battery Backup for Load Shedding: Questions Answered

How do I calculate how long my battery will last?

Runtime depends on three things: your battery’s usable capacity in kilowatt-hours, the efficiency of the inverter, and the load you are drawing in watts. As a working example, a 5kWh battery can supply 5kW of power for one hour, or 1kW for five hours. In practice you get less than the theoretical maximum because inverters are not perfectly efficient and most batteries should not be discharged to zero, so plan on a usable fraction of the nominal capacity.

What size inverter do I need?

Your inverter must be able to carry the maximum load you intend to run during an outage, not just the average. Add up the appliances you want to keep running — fridge, freezer, lights, router, television, and possibly a microwave or kettle — and remember that motors and compressors draw a surge of several times their running wattage when they start. Sizing the inverter exactly at your running load leaves no headroom for those surges.

What does a battery backup system cost?

A small system designed to keep the lights, router and a fridge running through load shedding typically starts at around R20,000 to R40,000. A larger installation capable of carrying most of a household’s needs for several hours runs from R60,000 to R150,000 or more, depending on battery chemistry, capacity and inverter rating. The battery is usually the single most expensive component, and its cycle life is what determines the long-term value of the installation.

Which battery technology should I choose?

Lithium batteries, and particularly lithium iron phosphate types, allow a deeper usable discharge and last for many more charge cycles than traditional lead-acid batteries. Lead-acid units cost less upfront but deliver less usable capacity for the same nominal rating and need replacing sooner. Over the life of the system the lithium option usually works out cheaper per kilowatt-hour delivered, even though the purchase price is higher.

Do I need solar panels as well as a battery?

Not strictly, but the combination changes the economics. A battery on its own is recharged from the grid, so it protects you from outages but does nothing to reduce your electricity bill. Adding solar panels means the battery is refilled each day at no cost, which cuts the amount you buy from the municipality and shortens the payback period on both components.