There’s your problem!
Batteries man… There are a lot of things that depend on batteries in our world, and some of them occasionally go ignored. Especially if they are in some sort of a backup scenario, like the UPS you see in the picture above. As you can see, not only are these well past their expiration date, they’ve also begun to swell an alarming amount. It’s always a good idea to mark the date of your last battery replacement on the outside of the enclosure, and set up some kind of system to remind you when their factory recommended refresh date is.