NERC Std PRC-005, Protection System Maintenance requires that battery continuity be verified every 18 months for all batteries, not having the monitoring attributes of Table 1-4(f). See Tables 1-4(a), 1-4(b) and 1-4(c) for vented lead-acid, valve regulated and nickel-cadmium batteries, respectively, in revision 2 of the standard which is the current version in force. The author has had many questions on how this verification can be made effectively. One of the simplest methods to verify battery continuity is to use a clamp-on ammeter set to ac to measure the ripple current passing through the battery at any point in the battery (i.e., anywhere from its positive to negative post or at the connection of the main leads to the battery). If ripple current, which is created by the battery charger when it rectifies ac to dc, is present, then the charge current from the battery charger is passing through the entire battery, assuring the battery conduction path is not open. If there is no ripple current present, either the charger is not in service or the battery is open and verification that the charger is operating is easily confirmed.
There are devices that can monitor battery continuity and these normally monitor other parameters as well. A photo of one such device is shown below (to enlarge photo, right click the photo and select “Open link in new tab”).
One another note, when battery continuity is verified, it does not provide assurance that the battery can perform its design function if required to do so. Other measurements and tests such as internal resistance and capacity testing provide that assurance, so do not become complacent and omit these critical measurements and tests. For example, the connections at the cell or monobloc posts can be severely corroded and although the battery will have continuity, it may not be capable of performing its design function. This is particularly true for battery types where the connection between cells in a monobloc are made by the battery manufacturer and the connections themselves are concealed from view (e.g., through-the-partition welds or connections made under the monobloc cover or connections that are filled with a potting compound once made). An example of such an issue is shown in the photograph that follows (to enlarge photo, right click the photo and select “Open link in new tab”). This post has been severely corroded in the seal well and although it will pass a battery continuity test, at this stage it would likely fail an internal resistance or discharge test.