Inverter VA vs battery Ah: how to plan home backup

Inverter VA and battery Ah answer different questions. The inverter’s ratings help describe the load it can support. Battery capacity is part of planning how long the chosen load can run. Neither number, on its own, tells you how many hours of backup you will get at home.

Before comparing products, write down the appliances that must keep working and the backup time you want. A shortlist built around that requirement is more useful than choosing the largest number on a product label.

Read VA, watts and Ah separately

Schneider Electric’s UPS selection guide distinguishes watt and VA ratings and explains that runtime changes with connected equipment. Its product examples concern UPS systems; do not transfer a particular model’s runtime to a different home inverter.

Prepare an essential-load list

Separate essential equipment from items you can leave off during a cut. Record the model, quantity and power information for each item. For networking equipment, include the fibre terminal or modem as well as the Wi-Fi router if both need local power.

Tell the installer about motors, pumps, refrigeration or other equipment with special starting requirements. Ask whether the proposed system supports those loads. A list containing only room names is not enough: two households with the same floor area can have very different backup needs.

Use our home backup planner to organise the requirement. The inverter size calculator provides a planning estimate from your inputs; confirm the proposed product’s actual continuous and starting limits with its manufacturer or installer.

Ask for runtime at your stated load

When someone promises “hours of backup”, ask which appliances are included, whether the battery starts fully charged and which battery configuration is assumed. Get the appliance list and assumptions written beside the runtime estimate. Otherwise, two sellers may be describing entirely different tests.

Record battery voltage, capacity, quantity and technology. Ask how battery condition and the system’s operating limits affect the estimate, and request the manufacturer’s runtime information where available. The battery backup calculator lets you explore assumptions; it is not a load test or a guaranteed runtime.

For a larger existing battery, do not assume compatibility with your inverter or charger. Ask the manufacturer or a qualified installer to confirm the permitted configuration. Do not change battery-bank wiring yourself.

Compare the complete system quotation

Ask for the exact inverter and battery models, the supported loads, installation work and warranty terms. Clarify where the system will be installed, who will assess the location, and which circuits will have backup. Follow the manufacturer’s installation and ventilation requirements rather than treating a storage corner as automatically suitable.

Also ask what happens when the mains supply returns, what maintenance is needed and who handles a fault. If changes to your home’s circuits are included, use the wiring quotation checklist to separate those costs from the equipment price.

A powered router does not guarantee internet access

Backup for your router keeps that local device powered. It cannot guarantee that your internet provider’s upstream equipment remains available. Check voltage, connector and polarity compatibility in the device and backup manufacturers’ instructions before buying a router UPS. Use the router UPS calculator for planning, then confirm the actual equipment match.

Common questions

Will a higher-VA inverter always give longer backup?

No. Its output rating and the complete battery system’s runtime are separate considerations. Compare the same appliance load and battery assumptions before deciding.

Should I keep everything on backup?

Start with what you need during the outage. Ask the installer which loads the proposed system can safely support. Adding appliances changes the requirement, so an earlier runtime estimate may no longer apply.