Backup Battery for 2013 iMac

If you go to the APC website they have a product selector that will help you pick what is appropriate for your situation. I just tried a few examples. You can select the type of device(s) you want to run on UPS. Note: they suggest an iMac will draw 136W, yet the Apple specs say 241W at Max. The 136W is probably reasonable for normal usage but if you pick 241W + some accessories you might be near 400W total. Using that figure, with a 30 min run time they are suggesting a UPS Pro 1500 ($400). If you want 1 hr run time they are suggesting a couple of options at $1000, and 4 hr run time starting at $1500. Most folks I know go for a minimum reasonable run time to keep costs under control. If you back off on Watts to the 136W load figure and look at the 300W unit you mention, you are looking at only about 20 minutes run time. They do get expensive quickly. Maybe go for the 300W unit and always turn it off if you are leaving the computer unattended(?).

APS units are well regarded here on this forum. However, one that will run your Mac "for days" would be insanely large & expensive. I'd probably select one that would run my gear for a hour or so and get a Generac whole house (or partial house) generator. No, I do not work for Generac but several of my neighbors have whole or partial whole house generators and the Generac unit is the quietest of all in the neighborhood.

I do not currently have a UPS, although I have in the past. Some users here have commented that they use the included software and others (like myself) prefer not to install the software on their Macs and simply let the UPS run as a standalone power supply. I did not see a major advantage to installing their software and prefer to not clutter the Mac with 3rd party software. Others may disagree and hopefully they will comment offering opinions explaining why.

When I was living in an area with lots of power outages and I simply got one that gave me enough time to quit whatever apps I had open - about 3 minutes. That keeps the purchase price reasonable. As well, I would make sure that I quit all apps if I left for some time and shut it down overnight or when I was going to be gone for 2 days or more. Doing it that way meant there was no need to worry about external drives, etc. - I would not run the printer during an outage anyway. And, most of them do not come with software that is compatible with Macs - you really do not need it anyway; as soon as you hook one up, it will show up in System Preferences and you can set the timing there.

You're welcome. Good luck with it !