As others have said, the batteries will be toast.
Sealed Lead Acid batteries as used in UPS units die two ways (outside of a catastrophic mechanical failure anyway).
A) Sulfation. If the cells are left under charged the lead sulfate that develops on the plates slowly turns into a much harder form which is for all intents and purposes impossible to reverse, leading to high internal resistance and the inability to re-charge. It does not take much undercharge to lead to sulfation.
B) Plate corrosion. This happens as a natural part of the charging process. A *lot* (like the majority) of UPS units float the batteries at the highest possible rated float voltage to try and extract the maximum runtime out of them. This naturally leads to plate corrosion, and as the plates corrode they lose active plate material reducing the quantity of charge the battery can hold.
So undercharge them and kill them with sulfation, overcharge them and rapidly corrode the plates or charge them properly as per the manufacturers data sheet and they'll die of one or both in time.
I too have some UPS batteries here that have > 10 years on them, but they are very expensive purpose built long life batteries and in a UPS that takes very good care of them (ie does not float charge, manages temperature and properly temperature compensates the charging voltage). Most consumer/prosumer/office UPS will kill a set of batteries in 3-5 years even with almost no discharge cycles purely by temperature and plate corrosion.
Batteries that have been left discharged (and they will self discharge pretty quickly even if left disconnected) for a matter of weeks will often be so sulfated as to be toast. If the UPS is worth saving, ehuck 'em and buy new ones.