Because batteries store large amounts of energy, there are certain hazards that
are associated with battery operation. These hazards must be fully understood to
ensure safe operation of batteries.
EXPLAIN the adverse effects of a shorted cell.
EXPLAIN how gas generation is minimized for
a lead-acid battery.
EXPLAIN how heat is generated in a lead-acid
Cell short circuits can be caused by several conditions, which include the following: faulty
separators; lead particles or other metals forming a circuit between the positive and negative
plates; buckling of the plates; or excessive sediments in the bottom of the jar. The primary cause
of some of these occurrences is overcharging and overdischarging of the battery, which causes
sediment to build up due to flaking of active material and buckling of cell plates.
Overcharging and overdischarging should be avoided at all costs. Short circuits cause a great
reduction in battery capacity. With each shorted cell, battery capacity is reduced by a percentage
equal to one over the total number of cells.
A lead-acid battery cannot absorb all the energy from the charging source when the battery is
nearing the completion of the charge. This excess energy dissociates water by way of electrolysis
into hydrogen and oxygen. Oxygen is produced by the positive plate, and hydrogen is produced
by the negative plate. This process is known as gassing.
Gassing is first noticed when cell voltage reaches 2.30-2.35 volts per cell and increases as the
charge progresses. At full charge, the amount of hydrogen produced is about one cubic foot per
cell for each 63 ampere-hours input. If gassing occurs and the gases are allowed to collect, an
explosive mixture of hydrogen and oxygen can be readily produced. It is necessary, therefore,
to ensure that the area is well ventilated and that it remains free of any open flames or spark-