How often do UPS batteries need replacing?

Most small single phase UPS with a standard 5 year design life valve regulated lead acid (VRLA battery will require a battery replacement around years 3-4 of operation. This assumes that the batteries are operated within an 20-25˚C ambient temperature range. Long runtimes and larger single single and three phase UPS systems using 10 year design life VRLA batteries will require replacement around years 7-8 of operation.