Examination of VRLA cells sampled from a battery energy storage system (BESS) after 30-months of operation

Valve-regulated lead-acid (VRLA) batteries continue to be employed in a wide variety of applications for telecommunications and uninterruptible power supplies (UPS). With the rapidly growing penetration of Internet services, the requirements for standby power systems appear to be changing. For example, at last year's INTELEC, high voltage standby power systems up to 300-V DC were discussed as alternatives to the traditional 48-volt power plant. At the same time, battery reliability and the sensitivity of VRLAs to charging conditions (e.g., in-rush current, float voltage and temperature), continue to be argued extensively. Charge regimes which provide "offline" charging or intermittent charge to the battery have been proposed. Some of these techniques go against the widely accepted rules of operation for batteries to achieve optimum lifetime. Experience in the telecom industry with high voltage systems and these charging scenarios is limited. However, GNB has several years of experience in the installation and operation of large VRLA battery systems that embody many of the power management philosophies being proposed. Early results show that positive grid corrosion is not accelerated and battery performance is maintained even when the battery is operated at a partial state-of-charge for long periods of time.