A:Answer Hi Lee,
Wow. I'm not sure about that. It will run a 27inch iMac while I'm working on the machine (so screen on and processors doing work) for about 70 to 80 min. However, if you're talking about just the modem and router for your internet, and maybe a small VOIP device, I would think much longer than that!! On APC's website, you can actually select the model of Back-Up unit you are interested in and then put in the information for how much power, the devices you are going to connect, draw and the website will calculate the "run time" for you.
Hope that helps.