There are plenty of factors which reduce the life of battery........Battery full cut off, deep discharge cut off, quality of Acid used, quality of water use to level the electrolyte, charging discharging frequency, use of battery, climatic conditions, etc......
I have seen many batteries dying within 1 year, and many running upto four years maximum so far......
you mentioned only AGS battery, yes.....its the No 1 quality battery manufactured in Pakistan.
As i experienced with UPS
1. AGS
2.Phoenix
3.Excide and FB ( Same company)
4. Volta and OSaka ( same company