C&D Technologies RS-1476 Standby Battery Vented Cell - Manual (Page 28)

CAUTION
RECHARGE BATTERIES AS SOON AS POSSIBLE AFTER A DISCHARGE. Failure to recharge batteries
promptly after a discharge may lead to sulfation or, in the case of deep discharge, to a complete battery
failure due to hydration. If charging at equalize voltage is not practical, recharge battery at float voltage.
2.3 Batteries retained on open circuit stand
As soon as a battery is removed from a charger, self-discharge begins. This is caused by internal losses in the cell.
Lead antimony cells lose charge at a faster rate than corresponding lead-calcium cells. Lead-calcium cells will self-
discharge at a rate of one to two percent a month. Therefore, if cells remain on open circuit (with no charging voltage
supplied) for prolonged periods, the affected cells may become sulfated and require corrective action. In most cases
an equalize charge is adequate to restore the cells/battery to a satisfactory operating condition. However in extreme
conditions when the battery is left on open circuit for a very long time, the cells may develop hard sulfate and never
fully recharge as mentioned in Section 2.2.
2.4 Hydrated batteries
When a battery has been over-discharged well beyond its design limits, and left in a discharged state, it is subject
to irreversible damage known as hydration. This is a phenomenon in which the specific gravity of the electrolyte has
been depleted to a value so low that it permits the lead components to go into solution, totally destroying the cells.
The reaction of dissolution forms many compounds and salts generically referred to as hydrate. These compounds
clog the separator pores and upon recharge, react to form metallic lead. As the process continues, thousands of short
circuit paths are created. Very often, the effect of the short circuits goes unnoticed except for an observed increase in
charging current. As the reaction proceeds, over an extended period of time, the short circuits become so extensive
that it is difficult to keep the cells charged. Finally, the cells may experience terminal short circuit failure.
The cells and cell components shown in Figures 4.2.4 and 4.2.5 exhibit the damaging effects of hydration. Hydration
can be avoided by the use of low voltage cut-out devices, which disconnect the battery from the load after the battery
is discharged at its specified load current and reaches its designed cut-off voltage. The battery must be recharged
as soon as possible. Battery hydration usually occurs when the load on the battery is much less than the design load
current, or when the battery is used without a low voltage disconnect during prolonged outages. This condition allows
the battery to discharge to a very low depth of discharge depleting the available acid ions in the electrolyte. The
specific gravity of the electrolyte finally approaches that of water.
Typically, if one or more cells in a battery become visibly hydrated, it is only a matter of time before the remaining cells
exhibit the same condition.
FIGURE 4.2.4 - Arrow points to white,
crystalline hydrate
PART 4
REFERENCE INFORMATION, TROUBLE SHOOTING & EXTENDED MAINTENANCE (CONTINUED)
FIGURE 4.2.5 - Cutaway shows clogged
separator with the by-products of hydration
SEPARATOR PLATE PLATE
RS1476/0215/CD 26 www.cdtechno.com