@Earl remove the buzzer, put an external battery connector on it, and use it with descent sized batteries!

@RueNahcMohr
Your idea is something I have considered, namely, connecting a bigger 12V battery and using the built-in inverter to convert 12V DC to 120V AC. But the #electronics built into this UPS might not be able to handle extended use and may overheat. I already have inverters designed for running bigger loads for an extended time, so I think it would be safer if I stuck with those. For now, I am using this old box as a power strip, extension cord, and surge protector only.