No mention at all of of ampere hours, just a manufacturer specific part number and this: "12v 36W/cell 15 min" The dimensions indicate something around 7Ah although the battery bay also contained a dummy battery of the same size.
The UPS was allegedly rated at 650VA (for how many seconds?) and had been in service for about 10 years. It easily held the PC up during numerous relatively short mains voltage dips until it had to cope with an extended power loss that didn't auto shutdown the PC.
But at least I could remove the battery without an angle grinder/axe/chainsaw as fortunately the UPS wasn't made by APC.