Battery terminals may sound unimportant to the inexperienced, but they are important to a mechanic because they can cause a multitude of problems. They are the main connection for the power to the vehicle and can produce a power drop from the terminal to the appliance or the buss bar. A buss bar is where the electrical current is distributed to the different parts of the car. A voltage drop is where there are 12 volts being applied at one end of a line and 11 volts or less at the other end of the same line. The types of material that are used also can make a major difference in current flow. Gold- or copper-plated terminals carry the best load.
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The basic contact points on battery terminals and the battery itself can corrode or have uneven contact enough to cause major voltage drops. A broken terminal or even the connection to the wire carrying the load or corrosion in the line itself can cause voltage drops. Corrosion on contact points will also cause voltage drops.
All of the early batteries up to the present day have had top terminals on the batteries. Many of the new vehicles with the redesigning for aerodynamics have lowered the bonnets and a top terminal battery is not feasible. Top terminals do not allow hood clearance so they have developed the side terminal for these applications.
There are currently three types of batteries with different terminal configurations. There is the old-style top terminal battery, where the battery terminals are located on the top of the battery; there is a battery with both top terminals and side terminals; and the third type is the side-terminal-only battery.
The top post battery has three types of terminals available. The lead conventional style and the lead type with a flat on the wire side with a stud and wing nut so that the battery can be disconnected without removing the battery terminals. Simply unscrew the wing nut and lift the wire off. There is also the gold-plated terminal for car stereo applications. This connector has the lowest voltage drop of all due to its dense molecular structure. Then there is the side terminal battery with a round terminal on the wire side with a bolt through it and a flat round surface on the side of the battery with threads for the bolt in the wire end. These terminals have significantly more problems with conductivity due to the bolt and lead plate used to attach to the battery. Care must always be taken with these to be sure there is no corrosion in between the bolt and the plate and the plate and the battery. Corrosion forms more often on these and causes more voltage drop.
Never tighten the bolt too tight in the battery since the threads are lead; if the bolts won't tighten down there will be a loose connection resulting in a voltage drop. Always put grease on the terminals to prevent corrosion. Always check the positive and negative wires for heavy corrosion in the plastic housing or insulation. Replace the wire if you see any corrosion.
Making a good inspection of the battery terminals and correcting any problems resulting in voltage drop will greatly improve the intensity of the lights. The battery will have a faster rate of charge resulting in a longer-lasting battery. This also will help to prevent no-start problems associated with poor ground terminals.