Operating experience with VRLA batteries in the Croatian PTT

Following a technology review in the late 1980s HPT introduced VRLA batteries into their expansion programme starting 1990. Croatia was affected by a war during the period 1992-1995 and at the conclusion of these hostilities HPT audited the performance of its power systems. The performance of VRLA batteries installed over the years 1992 to 1996 was determined for four regions in Croatia. These results have been compared to estimated performance values calculated from meteorological data supplied for the years 1992 to 1995. In general terms, the measured performance of the VRLA batteries has achieved the performance predicted from operational temperature derived from the meteorological statistical data. The exceptions to this conclusion occurred in the Gospic region, where random discharges of the batteries occurred which resulted in a 20% shortfall in performance. This was attributed to inadequate recharging in a cycling situation and may or may not be a permanent shortfall. As a consequence, plans are being considered to modify the float charging of these batteries in order to improve the charge acceptance of the batteries, and thereby eliminate the problem