Car Battery Guide

An automotive battery is a rechargeable battery that is used to supply electrical current to a motor vehicle. Its main purpose is to feed the starter, which is used to start the engine. Once the engine is running, power for the car’s electrical systems is supplied through the alternator.

Battery used in modern cars

Gasoline and Diesel engine

Usually, starting uses less than three percent of the battery capacity. For this purpose, automotive batteries are designed to deliver maximum current for a short period of time. They are occasionally referred to as “SLI batteries” for this reason, for Starting, Lighting, and Ignition. SLI batteries are not designed for the purpose of deep discharging, and a full discharge can reduce the battery’s lifespan.

As well as starting the engine, an SLI battery supplies an extra amount of power necessary when the vehicle’s electrical requirements exceed the supply from the charging system. It also acts as a stabilizer, evening out potentially damaging voltage spikes. While the engine is running, most of the power is given by the alternator, which includes a voltage regulator to keep the output 13.5-14.5 V. Modern SLI batteries are lead-acid type, using six series-connected cells to give a nominal 12 volt system (in most passenger vehicles and light trucks), or twelve cells for a 24 volt system in vehicles like heavy trucks or earth-moving equipment.

Electric cars

Battery electric vehicles are powered through a high-voltage electric vehicle battery, but they generally have an automotive battery as well, so that they can use standard automotive accessories which are made to run on 12 V.


An automobile battery is an example of a wet cell battery, having six cells. Each cell of a lead storage battery has of alternate plates made of a lead alloy grid filled with sponge lead (cathode plates} or coated with lead dioxide (anode). Each cell is filled with a sulphuric acid solution that is the electrolyte. Initially, cells each had a filler cap, by which the electrolyte level could be viewed and which allowed water to be added to the cell. The filler cap had a small vent hole which allowed hydrogen gas generate during charging to leave from the cell.

The cells are connected through short heavy straps from the positive plates of one cell to the negative plates of the adjacent cell. A pair of heavy terminals, plated with lead to resist corrosion, are mounted at the top and sometimes to the side of the battery. Earlier, auto batteries used hard rubber cases and wooden plate separators. Modern units use plastic cases and woven sheets to stop the plates of a cell from touching and short-circuiting.

Earlier, auto batteries required regular inspection and maintenance to replace water that was decomposed during operation of the battery. “Low maintenance” (sometimes known as “zero maintenance”) batteries have a different alloy for the plate elements, reducing the amount of water decomposed on charging. A modern battery may not need additional water over its useful life; some types remove the individual filler caps for each cell. A con of these batteries is that they are very intolerant of deep discharge, for instance when the car battery is completely drained by leaving the lights on. This coats the lead plate electrodes with sulphate deposits and it can reduce the battery’s lifespan by a third or even more.

VRLA batteries, also called absorbed glass mat (AGM) batteries are more tolerant of deep discharge, but are more expensive. VRLA batteries do not allow addition of water in the cell. The cells each have an automatic pressure release valve, to protect the case from rupture on severe overcharge or from an internal failure. A VRLA battery cannot spill its electrolyte which makes it specifically useful in vehicles like motorcycles.

Batteries are typically designed of six galvanic cells in a series circuit. Each cell gives 2.1 volts for a total of 12.6 volts at full charge. During discharge, a chemical reaction gives out electrons, making them flow through conductors to produce electricity. As the battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface into lead sulphate. When the battery is recharged, the chemical reaction is reversed: the lead sulphate is formed again into lead dioxide. With the plates restored to condition they were in before, the process may be repeated.

Some vehicles use other types of starter batteries. The 2010 Porsche 911 GT3 RS has a lithium-ion battery as an option to help save weight. Heavy vehicles might have two batteries in series for a 24 V system or may have series-parallel groups of batteries supplying 24 V.


  • Physical format: batteries are grouped by physical size, type and placement of the terminals, and also the mounting style.
  • Ampere-hours (A·h) is a unit which is related to the energy storage capacity of the battery. This rating is required by law in Europe.
  • Cranking amperes (CA): the amount of current that a battery can provide at 32 °F (0 °C).
  • Cold cranking amperes (CCA) is the amount of current a battery that can provide at 0 °F (−18 °C). Modern cars with computer controlled fuel-injected engines take not more than a few seconds to start and CCA figures are less important than they were in the days of carburetors.
  • Hot cranking amperes (HCA) is the amount of current a battery can give at 80 °F (27 °C). The rating means the current a lead-acid battery at that temperature can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery).
  • Reserve capacity minutes (RCM) is a battery’s ability to take a minimum stated electrical load; it means the time (in minutes) that a lead-acid battery at 80 °F (27 °C) will repeatedly deliver 25 amperes before its voltage drops below 10.5 volts.
  • Battery Council International group size (BCI) says a battery’s physical dimensions, such as length, width, and height. These groups are made by the organization.
  • In the USA, there are codes on batteries to help consumers buy a recently produced one. When batteries are stored, they can then start losing the charge. A battery made in October 2015 will be having a numeric code of 10-5 or an alphanumeric code of K-5. “A” is for January, “B” is for February, and it goes on (the letter “I” is skipped).
  • In South Africa the code on a battery to indicate production date is part of the casing and shown on the bottom left of the cover. The code is Year and the week’s number. (YYWW) like, 1336 is for week 36 in the year 2013.

Use and maintenance

Excess heat is a major cause of battery failures, as when the electrolyte evaporates because of high temperatures, decreasing the effective surface area of the plates exposed to the electrolyte, and leading to sulfation. Grid corrosion rates increase depending on the temperature. Also low temperatures can cause to battery failure.

A vehicle having a flat battery can be jump started by the battery of another vehicle or by a portable battery booster, after which a running engine (but faster than idle speed) will continue charging the battery.

Corrosion at the battery terminals can stop a car from starting due to electrical resistance, which can be prevented by the proper application of dielectric grease.

Sulfation occurs when the electrodes become coated with a hard layer of lead sulfate, which weakens down the battery. Sulfation can take place when battery is not fully charged and remains discharged. Sulfated batteries should be charged slowly in order to prevent damage.

SLI batteries are not made for a deep discharge, and their life is reduced when subjected to this.

Car batteries using lead-antimony plates need regular topping-up with pure water to replace water lost due to electrolysis and evaporation. By changing the alloying element to calcium, more recent designs have led to the reduction of the rate of water loss. Modern car batteries have decreased maintenance requirements, and may not provide caps for addition of water to the cells. Such batteries have extra electrolyte above the plates to allow for losses during the battery life.

Some battery manufacturers have an in-built hydrometer to show the state of charge of the battery.

The primary wear-out mechanism is the shedding of active material from the battery plates, which gets collected at the bottom of the cells and which may eventually lead to short-circuiting the plates. This can be substantially reduced through enclosing one set of plates in plastic separator bags, made from a permeable material. This allows the electrolyte and ions to pass through but makes sure to keep the sludge build up from bridging the plates.

Environmental impact

Battery recycling of automotive batteries decreases the need for resources required for the manufacture of new batteries, diverts toxic lead from landfills, and prevents the risk of improper disposal. Once a lead acid battery ceases to hold a charge, it is called a used lead-acid battery (ULAB), which is classified as hazardous waste under the Basel Convention. The 12-volt car battery is the most recycled product in the whole world, according to the United States Environmental Protection Agency. In the U.S. alone, about 100 million auto batteries a year are being replaced, and 99 percent of them are turned in for the purpose of recycling. However the recycling might be done incorrectly in unregulated environments. As part of global waste trade ULABs are shipped from industrialized countries to developing countries for the reason of disassembly and recuperation of the contents. About 97 percent of the lead can be recovered from it. Pure Earth estimates that over 12 million third world people have been affected by lead contamination from ULAB processing.


Fortunately, there are a few symptoms that may show that your battery needs attention. Before it’s too late, just –

  1. Slow Engine Crank: When you try to start the vehicle, the cranking of the engine is sluggish and takes longer than normal to start.
  2. Check Engine Light: The check engine light might sometimes appears when your battery power is weak.
  3. Low Battery Fluid Level: Car batteries usually have a part of the casing that’s translucent so that you can always keep an eye on your battery’s fluid level. If the fluid level is below the lead plates: (energy conductor 🙂 inside, it’s time for the battery and charging system to be tested.
  4. The Swelling, Bloating Battery Case: If your battery casing looks like this you can blame excessive heat for making your battery case to swell, decreasing your battery’s life.
  5. Battery Leak: Leaking also results in the corrosion around the posts : (where the + and – cable connections are located.: ) The gunk might need to be removed; otherwise, your car won’t start.
  6. Old Age: Your battery can last more than three years but, at the very least, have its current condition inspected on a yearly basis when it reaches the three-year mark.

How to Change a Car Battery

Pull your gear together — an adjustable wrench, clean lint-free rags, a pair of disposable latex gloves, some water and baking soda, a battery brush, and an inexpensive pair of the safety goggles. These steps help you change a car battery:

Turn off your engine.

Make sure that your vehicle is parked, with the engine shut off and the parking brake on.

Open the hood and place a blanket or pad on the fender.

This will protect your car from corrosive battery acid.

Remove the cables from the battery terminals.

Look in your owner manual to check whether your vehicle has negative ground. If it does, use an adjustable wrench first to loosen the nut and bolt on the clamp that holds the battery cable on the negative terminal. (That’s the post with the little “–” or “NEG” on it.) If your vehicle has a positive ground, just loosen the cable with “+” or “POS” on it first. Remove the cable from the post and keep it out of your way. Then remove the other cable from its post and also lay that aside.

If you have trouble loosening the bolt, hold it with one wrench and the nut with another, and move the wrenches in opposite directions. In this case, you wouldn’t want to remove the bolts; just loosen them to release the cable clamps.

Remove all the devices are holding the battery in place.

When you’re removing a bolt or screw, after you’ve loosened it with a tool, turn it the last few turns by hand so that you have a firm grip on it when it becomes loose and it does not drop and roll into obscurity.

Remove the battery.

When the battery is free, lift it off its seat and place it out of your way.

(If the tray on which the battery was standing is rusty or even has deposits on it, clean it with a little amount of baking soda dissolved in water)

Wear your gloves as the battery stuff is corrosive, and be sure the battery tray is completely dry before taking the next step!

Place the new battery on the tray.

Make sure it is in the same direction as the old one was.

Replace the devices that were holding the old battery in place.

Try to wiggle the battery to see if it’s completely secure.

Replace the battery cables on the terminals in a reverse order from which you removed them.

If your vehicle has negative ground, first, the positive cable goes back. Make sure that the clamps holding the cables on the battery terminals are gripping the posts tightly.

Take the old battery to a recycling centre that accepts batteries.

Batteries are filled with a toxic, corrosive liquid and must be disposed of in a proper manner. What’s more, old batteries are usually rebuilt into new ones, therefore, just throwing one in the trash is doubly bad for the environment. If you have your new battery installed when you buy it, the shop will recycle the old battery for you.

Video of How to change your battery in the right way

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