Stationary back-up and standby batteries (UPS)

Back-up batteries are cyclic use batteries; Deep discharge transforms the lead oxide on the positive plate into lead sulfate. Since the volume and weight of lead sulfate are greater than that of lead oxide, during rapid charging it will also detach active mass particles from the plates, which will lead to a decrease in battery capacity with the number of charging cycles. For this reason, back-up batteries have thicker plates to achieve better adhesion of the active mass to the grids. Also, to increase reliability, it is recommended to discharge the batteries to 80% of their nominal capacity (to avoid thickening of the plates with lead sulfate), and charge them with currents of approximately C/10 (where C is the battery capacity in Ah). If operating conditions cannot comply with these recommendations, instead of free acid batteries, AGM, GEL or tubular plate batteries are used.

Standby batteries are used in standby mode (buffer); they are permanently under charge, therefore highly susceptible to corrosion and abrasion (a phenomenon that occurs at the end of charging by the decomposition of water into hydrogen and oxygen bubbles); they are generally used to power computers, telephone exchanges, alarm systems, and emergency lighting when the mains power is interrupted. Because the number of cycles (charge-discharge) is not eloquent, the lifespan is expressed in years (approx. 5 years for an AGM battery).

Also, to make an optimal choice, you must take into account the fact that during the process of charging lead-acid batteries with free acid, especially due to excessive charging, the phenomenon of gasification occurs (electrolysis of water – release of hydrogen and oxygen bubbles). Through this phenomenon, the accumulators lose water, which must be replenished later, and the gases released cause an explosive atmosphere. Therefore, in rooms where large capacity batteries are located, it is necessary to either install gas detection and evacuation systems or use VRLA batteries. These are sealed batteries that have a cover designed to retain and recombine hydrogen and oxygen, resulting in water that returns to the battery. For applications requiring deep discharges and high charge-discharge currents, this type of case is combined with AGM technology, which immobilizes the electrolyte in fiberglass separators. This technology allows for a faster exchange of ions between the positive and negative plates and the ability to recombine the oxygen and hydrogen released at the end of the charging period, making this battery maintenance-free. Another advantage would be that the batteries will not leak, even if their casing is cracked. Another maintenance-free battery variant, from which the electrolyte cannot flow in the event of a crack, was patented in 1957 by the Sonnenschein factory. The electrolyte was immobilized (gelled) by adding silicon dioxide, forming a mass with the consistency of petroleum jelly.