How often should battery impedance testing be carried out?

The best frequency for impedance testing depends on the battery type, the site conditions and previous maintenance practices. The IEEE 11888 standard for VRLA batteries recommends, for example, that a baseline impedance measurement is made six months after the battery has been put into service, and that further impedance measurements are made at quarterly intervals there-after.

For NiCd and flooded lead-acid batteries, Megger recommends impedance testing at six monthly intervals. Impedance measurements should also be made immediately before carrying out every capacity test.