Valve-regulated batteries in standby application

Valve-regulated lead-acid batteries (VRLA batteries) nowadays are commonly used for standby applications. They offer quite a number of advantages compared to their flooded counterparts. There are, however, some limitations which should be noted. Water loss, for example, is an aging factor that cannot be compensated for by refilling. Even when a perfect internal-oxygen cycle is established, a certain water loss remains because of the unavoidable secondary reactions of hydrogen evolution and grid corrosion. The design of the battery and the operating conditions must aim to minimize this water loss. Beyond that, the rates of hydrogen evolution and grid corrosion have to be in a certain balance, because the polarization of the positive and negative electrodes is determined by this balance. If it is disturbed by a too high hydrogen evolution, it may happen that the negative electrode gradually will be discharged, even while the cell is floated at the correct voltage. Past experience has shown that such a balance cannot always be achieved. The insertion of a catalyst is an effective remedy to stabilize the polarization of the negative electrode