What’s a Car Battery?

What’s a Battery?


Car battery maintenanceThe first documented battery that used two dissimilar metals with an electrolyte between them was invented in 1800. Known as the voltaic pile after its ­inventor, Volta, this early battery consisted of copper and zinc discs piled on top of each other, separated by a layer of cloth or heavy paper soaked in a brine solution. Unlike the Leyden jar from much earlier attempts at energy storage, the voltaic pile produced a continuous and stable current level. The first rechargeable lead-acid battery for commercial use was invented by French physician Gaston Planté in 1859.

The Basics

The lead-acid battery is made up of plates, lead and lead oxides with various other elements that change the density, hardness, porosity and electron flow. Typically, the electrolyte solution will contain 35% sulfuric acid and 65% water. This solution causes a chemical reaction that produces electrons. As the battery charges, the sulfuric acid gets heavier, causing the electrolyte’s specific gravity (SG) to increase. As the state of charge (SOC) decreases through discharge, the sulfuric acid is pulled from the electrolyte and binds to the internal plates, forming lead sulfate. The density of the electrolyte becomes lighter and more water-like, and the SG is reduced.

Car battery serviceBattery sulfation starts when the SG falls below 1.225 or the voltage measures less than 12.4 (12-volt battery) or 6.2 (6-volt battery). Sulfation hardens the battery plates, reducing the electron flow and eventually reaching a point where it cannot be restored by recharging.

Battery life varies depending on the application as well as how the battery is used, ranging anywhere from six months to 48 months. Statistically, less than 30% of automotive batteries ever reach the 48-month mark.

Battery Types

There are two basic types of batteries: starting (cranking) and deep-cycle (marine, golf cart, forklift). A battery’s gravity varies depending on the battery type. Deep-cycle batteries use a denser electrolyte with an SG of up to 1.330 to get maximum runtime; aviation batteries have an SG of 1.285; traction batteries for forklifts are at 1.280; starter batteries come in at 1.265 and stationary batteries are at a low 1.225.

The starting battery is designed to deliver a high-energy output for a short amount of time and generally have a greater plate count. The plates will also be thinner (more surface area) and have somewhat different material composition. The deep-cycle battery provides less surge energy but a greater long-term delivery. Deep-cycle batteries have thicker plates and can be discharged well below their full charge level and recharged back to full. Car (starting) batteries don’t have that capability.

Battery Ratings

Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at 0° F for 30 seconds and not drop below 7.2 volts. So, a high CCA battery rating is good, especially in cold weather.

Cranking amps (CA) is measured at 32° F. This rating is also called marine cranking amps (MCA). Hot cranking amps (HCA) is seldom used any more but is measured at 80° F.

Reserve capacity (RC) is an important rating. This is the number of minutes a fully charged battery at 80° F will discharge 25 amps until the battery drops below 10.5 volts.

Amp hour (AH) is usually found on deep cycle batteries. If a battery is rated at 100 amp hours, it should deliver 5 amps for 20 hours, 20 amps for 5 hours, etc.

Corroded BatteryBattery Maintenance

Seventy percent of battery problems are caused by dirty and loose connections, so cable connections need to be clean and tight. Distilled water is best for filling a battery. Tap water is loaded with chemicals and minerals that can be harmful to a battery, but it’s a better option than no water at all.

Don’t overfill battery cells, especially in warmer weather. The fluid will expand in the warmer temperatures as well as when it’s fully charged. The battery charging produces gases that escape out the vent holes in the caps, condense on the metal parts and cause corrosion. Using corrosion prevention pads, sprays or grease (Vaseline works well) on or around the terminals will reduce the buildup. Also, make sure to keep the hold down brackets painted and clean to prevent them from deteriorating.

Cleaning the corrosion buildup is simple chemistry. A base solution reacts with an acid, and the idea is to remove the acid and corrosion without damaging the base metals. There are several over-the-counter sprays and solutions that work well for removing any corrosion or acid build up. Some technicians just use baking soda and water or a cola as a cleaning agent. Start with a baking soda and water mixture poured over the area, then rinse thoroughly, dry and apply some form of a preventive measure to avoid any buildup in the future. This includes repainting any metal brackets or exposed metal in the surrounding area as well.

How a battery worksCharging and Testing

A freshly charged battery is not a good candidate for checking the charge level. There will be a surface charge that hovers on the surface of the cells and is not part of the storage level of the battery itself.

If the battery has been sitting for at least 6 hours, you may begin testing. To remove the surface charge, the battery must experience a load of roughly 15 to 20 amps for about 3 minutes. Turning on the headlights (high beam) will do the trick. After turning off the lights you are ready to test the battery.

When you’re testing a battery with a hydrometer, you are actually measuring the amount of sulfuric acid in the electrolyte. If the reading is low, there’s not enough sulfuric acid in solution. Recharging the battery creates a chemical reaction to break up the sulfated bond between the plates and the acid, which allows the sulfuric acid to go back into the solution.

SOC SG   12V  6V
100% 1.265 12.7 6.3
75% 1.225 12.4 6.2
50% 1.190 12.2 6.1
25% 1.155 12.0 6.0
Discharged 1.120 11.90 6.0

Load testing is another way to determine the condition of a battery. Using a carbon pile type battery load tester, apply a load equal to one half the battery’s CCA level for 15 seconds. A good battery will not fall below 9.6 volts during the test and, when the 15 seconds has passed, the battery should return to the original starting voltage it had before the test.

The newer “non-carbon pile” battery testers work entirely different, and are highly accurate. They not only can spot a marginal battery much quicker, but also take into account the temperature and estimated battery life when calculating the overall condition. Interstate’s ED-18, for example, has a digital screen with all the functions clearly shown, as well as a printer built into it.

charging a batteryNew Lead Acid Systems

Lead acid batteries continue to be the most viable source of energy for most automotive applications. Some improvements have been made, and some claims are so promising that they sound too good to be true. A few of the new lead acid developments include systems and designs from Firefly Energy, Atraverda Bipolar, Axion Power, CSIRO Ultrabattery and EEStor.

Most of these developments are based on ceramics and other exotic metals and chemical combinations. Most of these “testing stage” ideas still use some form of lead-acid-based electrolyte solution. Is a new version of the wet cell battery with a longer charge rate and a longer life span coming the industry’s way?

The advancements in energy storage make it possible for new designs and new systems. Just think where we would be without the ability to store energy in a portable device such as a battery.

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