FACTORS THAT INFLUENCE RELIABILITY AND BATTERY LIFE

All batteries gradually wear out with use. This is caused by the wear and tear of repeated cycling of the active material and by corrosion of the lead grids or spines. Flat pasted plate batteries and tubular batteries have different operational characteristics and different wear-out mechanisms. These will be discussed in some detail so that these differences can be understood.

ACTIVE MATERIAL DENSITY

The density of the active material in the battery plates has a major influence on both the capacity and the life of the battery. It is important that the correct density is chosen and also that the density is constant over the entire plate. Too high an active material density causes

low capacity while too low a figure causes early failure. Additionally, if the density is variable, this causes uneven discharge and charge in the plates which can also result in the battery wearing out prematurely.

In the flat plate design the density of the active material is controlled by the paste density which is automatically made in the paste mixing machines to a controlled value. The density of active material in the plate is also extremely uniform since it is applied automatically by pasting machines.

On the other hand, the tubes of a tubular plate are filled by a method which involves the vibration of the plate at high frequency while a mixture of red lead and lead oxide powder is fed to the tubes. The purpose of the vibration is to prevent the oxide powder mixture from clogging and to assist its flow into the tubes. As the plate is filled, the oxide at the bottom tends to be tamped down by the action of the vibration and by the weight of the oxide at the top.

Consequently, the oxide is more dense at the lug end of the plate. This variation in density results in uneven discharge and charge of the active material which can cause premature failure. In extreme cases, which will be referred to later,the extremely dense material at the top of the plate can burst the retaining tube which results in severe shedding with a consequent capacity loss.