A 25th cell in a 48 volt telephone battery plant. Float, capacity and recharge behavior after a one year field trial in a working telephone central office environment

The effect of low float (2.10 Vpc; 40 mV positive polarization) on a battery cell performance, and the improvement in battery plant capacity resulting from the addition of a 25th cell into a 48 volt battery string are discussed. Results of laboratory tests extending beyond one year and a one year field trial in a working telephone office are reported. Field trial results show that the initial one-hour improvement in capacity, resulting from the addition of the 25th cell, is retained after 7 months at low float, despite significant self-discharge of the negative plate. Quantitative rates of negative self-discharge, measured both in the laboratory and in the field trial, appear to remain essentially constant at 0.04-0.06 amp, for periods greater than one year, without regard to the length of time on low float. After more than one year at low float, there are indications that the shape of the discharge curve has begun to be affected by the significant negative self-discharge, but the effect on cell capacity remains minimal.<>