BATTERIES

A battery is an electrochemical device that stores chemical energy and converts it into electrical energy. It's function is to provide electrical power independent of power systems or equipment.

Batteries are provided in many shapes and sizes. However, they are classified into two specific categories:

Primary Battery - one which cannot be recharged
Secondary Battery - one which can be recharged

Primary batteries are discharged once and discarded. Other than proper storage, there is no special care required to obtain full life expectancy. On the other hand, secondary batteries are rechargeable and do need special care in order to provide power for their full life expectancy.

This covers basic information on batteries - conditions which shorten their life expectancy, preventative maintenance to insure full life, and the replacement of defective batteries with current replacement batteries.

There are four major types of batteries generally used in emergency lighting: gel lead, pure lead, lead acid, and nickel cadmium. In general, all batteries consist of a container, some form of electrolyte and two electrodes (metal plates). The difference between the various types is the composition of the electrolyte and the type metal used in making the electrodes.

Gel Lead
These batteries are a form of lead acid batteries, except that the electrolyte is in a gelatin form. Some are designated as lead-calcium and some as lead-dioxide depending on the material used in constructing the electrodes (plates).

Pure Lead
These come as cylindrical cells of two volts each. The cells contain spirally wound plates of pure lead, hence the name. Looking like big flashlight batteries, they are easily recognized and come in various sizes.

Lead Acid
These are "wet cell" batteries with a diluted sulfuric acid liquid and lead plates of several possible variations. They can carry identifications such as: Lead Antimony, Lead Calcium, Maintenance Free, Long Life Lead and Medium Life Lead. These designations refer to construction variations and material used in forming the plates.

Nickel Cadmium
These batteries are of the highest quality. They are alkaline nickel cadmium cells with a potassium hydroxide electrolyte. They can easily be recognized since the individual cell rate is 1.2 volts.

BATTERIES - TECHNICAL INFORMATION

A battery is rated under ideal conditions, however, in actual use, these conditions are not always met. Changing temperatures, over charging, under charging, deep discharge and physical abuse will affect the performance of a battery. Let's look at what effect, if any, these conditions have on batteries.

Temperature
Ideally, batteries should operate with the temperature range to 60 - 80 degrees F to obtain optimum performance and help extend battery life. Although capacity improves significantly as temperature increases, battery life also deteriorates as temperatures rise above 80 degrees F rapidly. Temperatures lower than the optimum operating range can be used to prolong battery life (storage and shelf life), however, it will reduce available capacity and battery operating time.

Overcharge
Causes continued high current flow after a full charge is attained. The water of the electrolyte is decomposed and the battery will age prematurely. Excessive water loss indicates overcharge.

Undercharge
Causes the current flow to essentially stop before the battery is fully charged. This allow some of the lead sulfate to remain on the battery plates which can eventually reduce the available capacity of the battery by causing sulfation and plate damage.

Deep Discharge
Can cause the battery to be damaged and impair performance if discharge is continued after the terminal voltage falls below 80% of nominal. Deep discharging a battery past its designed end volts can cause the active paste to loosen from the surface of the plate grid so that the plate will no longer be able to receive a subsequent charge.

Physical Abuse
Can shorten life expectancy and/or impair the performance of a battery. Some examples:

A. Storing batteries in excessively warm locations can cause accelerated self discharge and affect active plate materials.

B. Storing batteries directly on concrete or dirt floors will also accelerate self discharge.

C. Dropping a battery can cause internal and/or container damage.

D. Avoid commercial battery "rejuvenator" solutions which can cause batteries to degrade.

E. Tap water contains impurities, so use only approved distilled or de-ionized water to maintain electrolyte levels.

F. Loose connections, as well as making or breaking connection while batteries are in use can cause heat up and damage to the connectors and/or terminal posts.

G. Shorting a battery can also cause damage to the terminal post as well as internal damage to the battery.

H. Battery failure can also occur from shallow charge/discharge cycles and the battery appears to have lost capacity. This is sometimes referred to as "memory" effect. It is rarely seen, and only occurs with sintered style Nicad batteries.

Aside from failures due to normal age deterioation, more conditions leading to battery failure can be prevented or minimized through proper storage, installation and maintenance. Before storing a battery, a pre-storage check for possible damage or electrolyte leakage should be performed. Batteries should always be fully charged and stored in a clean, cool (60-70 degrees F), dry area away from potential sources of heat or external ignition, such as heating units, direct sunlight or adjacent electrical equipment. When battery leads and/or intercells are needed, they should be of the correct thickness needed for the applied load current. Care should also be taken that the correct "battery connection diagram" is used to install the batteries before making connections. When connecting, care should be taken that all contact surfaces, particularly the connecting posts, are clean. All connections should be tight and resistance free.