Ouch! Whats really weird is that I just had to replace 2 UPS last week. They were bought at the same time for use on my computer and home entertainment system. The batteries in both went out within a day of each other. They were almost exactly 4 yrs old. Got 2 new UPS as the batteries cost about the same as new ones.
Not terribly uncommon as the cell ages and dries out - builds up heat/gas & swells. We see it a lot...