Solar battery calculator for backup runtime
Choose a battery size and the appliances you want to keep on. This off grid battery calculator gives an honest starting estimate, not a promise of runtime.
How long will your battery last?
Pick a battery size and what you want to keep running.
Rough estimate at ~90% usable depth. Real runtime depends on the exact appliances and battery. A quote sizes it properly.
Get a battery quoteActual backup time changes with appliance cycling, battery condition, inverter losses, battery temperature and how much charge is available at the start of an outage. Use the result to shape the conversation, then have the final system designed around your home.
Use this tool on your own site
Journalists, bloggers and installers are welcome to quote or embed this tool free of charge. We only ask for a link back to the original so readers can check the working.
Figures, charts and calculator outputs on this page may be reproduced, in whole or in part, with clear attribution and a link to https://www.solarguide.co.za/calculator/battery-backup-runtime/. Last reviewed 3 September 2026. If you need a specific cut of the underlying assumptions for a story, email hello@solarguide.co.za.
Use the result properly
Keep the list to the circuits that matter in an outage. If a high-power appliance is essential, mention it in the quote request so the inverter and battery are assessed together.
Next step
Compare battery capacity, cycle life and warranty, then request a quote with your backup priorities included.
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