Debunking the Battery

By Glen Beanard technical contributor

The Purpose of the Battery

In the automobile, the battery serves three main functions. First is the obvious. It supplies electrical power for the ignition system, starter, computer system, and every other electrical component while the engine is not running (or any other instance when the alternator is not charging). Second, it serves as a reserve power source, should the electrical demand in the vehicle exceed that of what the alternator can produce. Finally, it serves as a damper or stabilizer for any electrical pulses. It absorbs high voltage spikes, and fills in between moments of low voltage. That action helps to smooth out the electrical noise in the system. Without that electrical dampening action, delicate electronic components could be at risk of damage from electrical spikes.

Electricity 101

Before we get in to talking about the battery, we need cover a few basics.

First, we must define some of the terms that will be used later. These terms are

Electricity , Amps , Volts , and Resistance .

The first term to identify is, ironically, the most difficult one; Electricity. That term actually has more than one definition. For the scope of this article, my definition will be that electricity is a supply of atoms with excessive electrons. Therefore, the flow of electricity is the exchange of electrons from one atom to the next. If those extra electrons are not flowing, then that would be static electricity. The terms amperage and voltage are used to measure the flow of electricity. Amperage is a measurement of quantity, whereas voltage is a measurement of pressure. Some atoms are more willing to share their electrons than others. Materials that are made out of atoms that will freely pass along electrons are referred to as conductors . These are materials such as metal and water. Some materials are made up of atoms that don t share their electrons as easily, like rubber, air, and plastic. Those materials, for the scope of this article, are referred to as insulators . Conductors have a lower resistance than insulators. You should note that all materials, even those that are considered insulators, will conduct electricity if there is enough voltage to force the electrons to exchange from atom to atom.

Amps, volts, and resistance are connected to each other in terms of effect. For illustration of this effect, picture a generic roadway. The actual speed the moving vehicles can represent voltage . The number of vehicles on the road at the same time can represent amperage . The posted speed limit on the road can represent the intended resistance of a circuit. The number of potholes on the road s surface can represent any unwanted resistance .

If you were to stand at the edge of the road and count the cars as they passed by, as long as there was a steady stream of vehicles, you would count more over a minute s time if they all sped up; right? In most cases, if you increase the volts, you will increase the amps that pass through the circuit. If you add resistance, the volts and amps will reduce. There are some exceptions to that. Just because the cars are moving faster doesn t mean there will always be more. They can have gaps between them. The same is true for electricity. Just because you have 12 volts, doesn t mean there will automatically be a lot of amps available. Keep that in mind as much electrical testing depends on that knowledge. Since 12 volt car batteries are rated by CCA. The number of amps that a battery can deliver at 70 F/26 C is called the battery s CCA rating (Cold Cranking Amps).

How and Why It Works

I m sure most of us have explained a battery to our customers as being simply a storage unit, much like a glass of water. That may be fine for our customers, however, as technicians, a more in depth explanation may be required. That is what I hope to provide.

A car battery is actually more of a little electric generator than a cup . It stores energy in a chemical form, then transforms that stored chemical energy into electrical energy on demand. A lead/acid battery has 2 different types of lead plates submersed in an electrolyte to make this possible. Lead Dioxide is the material used to make the positive (+) plates. The negative (-) plates are made from Sponge Lead. The plate is a lead alloy mesh grid (used as a framework) with Lead Oxide pasted onto the grid. The paste used for the negative plate has expanders added to it. The 2 types of plates are later formed into sponge lead (-) and lead dioxide (+) during the initial charging process after complete assembly of the battery. The two types of plates are stacked together with separators between them. The separators are porous and allow ionic current flow between the plates, but don t allow the plates to directly touch each other. The assembled plates and separators form an element . Each element has two connectors on top of it, one for positive, and one for negative. The elements are lowered into the battery case where they will have there own divided cell space and submersed in the electrolyte. They don t rest directly on the floor of the case. Rather, they rest on a honey comb of plastic walls molded in the bottom of the case. The elements are wired to each other by their appropriate polarity connector using straps. The straps are joined with the appropriate terminal (post) of polarity. The electrolyte is made from a mixture of water and sulfuric acid. All of those elements are necessary for the battery to function. All of those materials are depleted with time and usage, even the water used in the electrolyte.

During the discharge half of the cycle, sulfate from the electrolyte bonds with the positive and negative plates to form a layer of lead sulfate on them. Also, the oxygen in the positive plate combines with hydrogen in the sulfuric acid to form water. It is during this chemical reaction that electricity is produced out of the chemicals. As both plates become lead sulfate, the performance of the battery is reduced. It is also important to understand that the chemical reaction can only take place on the surface area of the plates where the electrolyte comes in direct contact with it. Since the acid is replaced by water during the discharge, the performance of the battery will decline as that occurs. However, you will notice that the battery bounces back after the load is removed because the electrolyte will circulate around in the cell. In which case, the plates will once again come in contact with the stronger electrolyte.

One discharge and recharge together form one cycle . We ve discussed what happens on the discharge half of that cycle. Now for the recharging half. Recharging the battery causes the sulfate to leave the lead and reform with the electrolyte. The plates and the electrolyte undergo some permanent changes during the cycle, not everything can be restored by simply recharging it. One thing that happens during the recharge is that hydrogen gas is being released at the positive plates, and oxygen is being released at the negative plates. These gasses were once elements used to make up the parts of the battery, and some amounts of them are vented out of it during recharge. Obviously, such a cycle can only occur a limited number of times before some of these elements are depleted

Another thing that is important to note, is that both hydrogen and oxygen are highly explosive. Care must be taken when handling a battery not to create sparks around it. Never remove the vents for charging a modern battery. Modern batteries have special vent designs that reduce the chance of explosion.

Lately, we ve seen a new (or new to us) battery design hit the part stores. They are spill proof batteries know as AGM batteries. Spiral/AGM batteries have the electrolyte in a glass mat media and are a member of the family of Valve Regulated Lead Acid (VRLA) batteries. The VRLA family of batteries includes the Gelled battery invented in the 60 s, and the Absorbent Glass Mat batteries invented in the 70 s. Although the spiral wound AGM batteries have been around since the 70 s, it seems like only recently that they have found a niche in the automotive market. That credit mostly belongs to the import street performance and off road performance enthusiasts who demand a battery that can be mounted inside the vehicle, be spill proof, and can be mounted in any position. They are among the lowest venting forms of lead/acid batteries. The plates and the glass media of a spiral/AGM battery are wound together and loaded vertically into cylindrical shaped compartments in the battery case. The spiral wound design also causes the plates to be physically reinforced against road vibrations. They surpass the conventional design in physical durability on higher CCA ratings. The reason for, is the fact that more plate surface area is needed for higher CCA rating. There is only so much room inside a battery. Therefore, in order to get more surface area on the plates, more plates are employed. The higher the number of plates in a limited space means they will be thinner, and by the same token, weaker. However, when the plates are wound around each other, they become reinforced. Plus, since the electrolyte is absorbed into a mat, it won t spill out if shaken or turned over like a conventional battery. That is something to keep in mind for the next off-road enthusiast that comes in needing a battery.

Testing Methods

The first test of a battery is a visual inspection. There are certain things a technician should look for when inspecting a battery. Some things to look for include the quality of the connection from the battery to the cables. Loose or corroded cables (potholes in the road) will hinder the battery s ability to supply the automobile with electricity. Likewise, a faulty connection will cause the battery to not receive a full charge from the alternator. Cracks or other leaks can cause acid spills. Missing battery hold down hardware can cause damage to the plates inside the battery from it being allowed to hop up and down from bumps in the road. No, a bungee strap doesn t count as hold down hardware. Dirt buildup on the top of the battery can actually cause a parasitic drain between the posts. So be sure to clean the top of the battery with battery cleaner. Missing factory heat shielding (insulators) will shorten the battery s life. As a guideline, every 15 F/8 C rise in temperature above 77 F/ 25 C will cut the battery life in half. A battery that might last for 10 years at 77 F/25 C will only be good for 5 years if operated at 95 F/33 C. Likewise, the same battery might only withstand a little more than one year at a temperature of 107 F/42 C. Have you ever seen a battery located directly behind or very near a radiator? Be sure to clean and reinstall all battery heat shields when replacing a battery. True, some batteries may have case designs that help protect it, but even still, the factory shielding should be left in place. Check to make sure that it is the right battery for the vehicle. Does it fit the tray? Does it interfere with hoses or wiring? Does the CCA rating at least meet the minimum CCA required as stated by the manufacturer of the vehicle?

One of the testing tools that can be used is a hydrometer. The problem however, is that it has become very impractical with today s batteries and vehicle designs. As a result, testing the specific gravity of the acid with a hydrometer is fast becoming a rarity in the real world of automotive repair. Therefore, I ll keep this part brief. At 80 F/26.7 C, if the specific gravity of the acid is 1.265 in each cell, then each cell is fully charged. At 1.225, it is 75%. At 1.190 it is 50%. At 1.55 it is 25%. Finally if it is 1.120 then it is flat dead. Again, those readings are at 80 F/26.7 C, temperature effects this measurement, so you will have to calculate temperature changes at different temps. Add or subtract 4 points (.oo4) for every 10 F above or below 80 F/26.7 C. If you are planning to use a hydrometer, please don t mix the acid between cells, wear safety clothing such as gloves and eye protection, and be careful not to drip acid anywhere on the vehicle. Some batteries already have a built-in hydrometer. The green eye in some brands of batteries is type of a hydrometer. The problem with those however, is that they only test the one cell they are mounted into. It is very possible to have that one cell test good , yet fail every other cell in the battery. The green eye is a wonderful idea, however, in my opinion, there should be one in each cell in order to be a trustworthy testing method.