A bog-standard Uninterruptible Power Supply. Available from multiple manufacturers (big names are e.g. Eaton, Schneider/APC, but there are lots of choices) in all sizes from "powers your desk light" to "powers your whole house/datacenter/emergency room".
Maybe there is value in marketing such a product to ordinary people that are not in IT or electrical engineering. Maybe you can improve on existing control interfaces and design. But don't be surprised when an established UPS vendor copies your product and crushes you with better numbers because of size.
I think this space needs some disruption. Most UPSs are dreadful. Cheap, lead-acid and unreliable. And the power banks with attractive specs that seem to be built around 100ah lifep04 batteries... they don't seem to work as UPSs. (and they're expensive)
