In one field trial, the performance of VRLAs in shallow-cycling remote photo-voltaic power systems in uncontrolled environments has been carefully watched over more than 7 years.
Capacity measurements were determined by annual capacity discharge tests.
As can be seen, two types of AGM VRLA and one type of gel 2V battery have all achieved at least 7 years service life.
The actual capacity measurement part of the trial ended in 1997, but the cells are still in-service. since the power system will raise low voltage alarms at 60% capacity, we can safely assume that after nine years all three types of batteries are still above 60%.
(Not bad for a technology that others say is not all that good!). But not all VRLAs can do this. Indeed, early in the trial some AGM monoblocks which were tried failed within 18 months.
