In my opinion, if we can buy a larger UPS, as we said at the start a larger UPS will have larger batteries, so a larger UPS running at 20% load will last longer than a smaller UPS running at 80% load. The second is to look for a UPS that has an external battery connector, that means the manufacturer offers an external battery for extending your runtime, and this is a safer, easier, and often more aesthetically pleasing option