This is truly rare and amazing opportunity, for some one to see from close, one APC UXBP24 battery box.
Theoretically two of those UXBP24 connected in series this is what SUA1000XL ups this is Max of what this is able to handle.
Secret of SUA1000XL this is it capability supplying 10A Max as charging current.
This current it is too much for a 24V 17Ah battery pair to handle, and no warning was given by APC back then, but for 38AH package 10A this is allowed for Fast charge.
UXBP24 this is four battery cells of 75Ah its one.
In a 24V pack all four them forming DC power source of 150Ah.
Configuration of two UXBP24 plus on-board battery of SUA1000XL them making sum of 317Ah.