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How to Replace Your Car Battery the Right Way

by Larry Carley copyright

There is a right way and a wrong way to replace a car battery. It's not a simple swap on late model vehicles because of the "keep alive" memories that are stored in many of your car's electronic modules and engine computer. If you just disconnect the battery without taking certain precautions, all of these stored and learned settings can be lost. So keep reading and we'll tell you everything you need to know to safely replace the old battery in your car.

Why Car Batteries Need to be Replaced

Car batteries have a limited service life, typically 4 to 5 years for wet cell lead-acid batteries, and sometimes as little as two to three years in a hot climate. Premature battery failure can occur if a battery is chronically undercharged because your vehicle is not drivenoften eough or far enough to keep the battery fully charged. It may take up to 20 minutes of driving to charge up a low battery. Idling for long periods of time with lights, heater, radio and other accessores on can run down a battery.

When your battery reaches the end of its service life, it may not accept or hold a charge, or it may not provide enough cranking amps to start your engine (especially during cold weather). Most batteries need to be replaced by the time they are 4 or 5 years old.

Batteries may also fail suddenly with no warning if an internal cell plate shorts out or breaks loose from the connector grid. This can be caused by severe vibration (driving lots of miles on extremely rough roads) or by mishandling (like accidentally dropping the battery on the ground).

Severe or prolonged overcharging can also ruin a battery by boiling away the electrolyte in the cells.

If your battery is getting weak, keeps running down or won't hold a charge very long, you should have the battery tested to see if it is good or bad. See BATTERY TESTING for details.

If your battery tests BAD, you need a new battery. However, it if tests GOOD, the battery may be running down because of a CHARGING SYSTEM PROBLEM or a KEY-OFF BATTERY DRAIN.


Several things to keep in mind:

Choose a replacement battery that has the same (or higher) Cold Crank Amps (CCA) rating as the original battery. A battery with a 600 to 700 CCA rating is a good choice for most vehicles. If you live in a cold climate and are concerned about reliable cold weather starting, choose a battery with a higher CCA rating.

Choose a replacement battery that is the same Group Size as your original battery. Group size refers to the dimensions of the battery (height, width and length) and the post configuration (side post, top post & location of the positive and negative posts on the battery). A battery that is the wrong size may not fit the battery tray of compartment in your vehicle.

battery label information
The battery label will tell you the battery amp ratings and Group size.
A separate sticker or label will tell you when the battery was manufactured.

Choose a replacement battery that is the same TYPE (or better) as the original. For most automotive applications, that would be a conventional wet cell lead-acid battery. If your original battery is an AGM battery, it should be replaced with a similar AGM battery, not a conventiona wet cell battery. An Absorbent Glass Mat battery contains no liquid, is spill proof, is more resistant to vibration damage, and generally lasts several years longer than an ordinary battery.

A standard wet-cell battery can be upgraded to an AGM battery to improve longevity and durability.

If you are replacing the battery on an older classic car or muscle car that is driven infrequently or stored over the winter, you might consider a marine deep cycle battery, RV battery or a yellow top spiral wound Optima battery that is designed for deep cycle applications.

For high performance or racing applications, another upgrade option would be to use a lightweight and compact lithium ion battery instead of a conventional battery or AGM battery. Lithium ion batteries can pack a lot of power into a smaller box to save space and weight, but they are also very expensive compared to other batteries.

If you are replacing the battery on a late model vehicle that has an idle stop-start system, or is a hybrid, and the original battery is an AGM battery, make sure the replacement battery is also an AGM battery. Do NOT substitute a less expensive conventional wet cell lead-acid battery for an AGM battery.

A more expensive "premium" battery usually comes with a longer warranty (typically 36 months or longer). A premium battery should outlast and outperform a standard replacement battery.


If your vehicle is less than 10 to 12 years old, AND your old battery still has power, DO NOT disconnect the battery until you have attached a battery saver, 12-volt charger or backup power supply to your vehicle's electrical system. For best results, connect the backup power supply or charger leads directly to the positive and negative battery cables. Make sure the clips on the leads are securely attached and don't slip off, and that the positive cable does not touch anything metal.

Disconnecting the battery on a late model vehicle will cause a loss of learned memory in various system modules. If voltage is not maintained to the electrical system while the battery is being replaced, some modules may require special relearn or reset procedures before they will function normally after a new battery is installed. See BATTERY DISCONNECT ISSUES for more info on this subject.

If your vehicle is more than 10 to 12 years old, using a battery saver or backup power supply is still and good idea but less essential. Disconnecting the battery without a backup power supply providing voltage to the electrical system while the battery is replaced will delete the PCMs learned fuel trim and idle settings, as well as saved radio and clock settings. However, the PCM will quickly reset itself and start to relearn the fuel trim and idle settings once the engine is restarted and the vehicle is driven. The radio and clock settings will have to be manually reset.

If you have an older precomputer car, or your old battery is completely dead (no power), there's no need to use a battery saver or backup power supply while changing the battery. Older cars have no modules or learned settings, and if the battery is completely discharged on a newer vehicle there won't be any learned settings to save. They will have already been lost.


Before removing the old battery, note the location of the positive (+) battery terminal and mark the polarity on the positive cable. This will help you avoid installing the new battery in a reversed position.

tighten battery terminals

Disconnect the battery terminal cables by loosening the screws on the cable clamps. Remove the negative cable first, then the positive cable.

Unfasten the battery hold-down strap. This is the metal strap that keeps the battery secured. Some batteries use a base clamp instead of a strap to hold the battery in place. If so, loosen the bolt that holds the clamp against the base of the battery.

Before you lift the battery out of your vehicle, put on a pair of latex or nitrile moisture proof gloves. These will protect your hands from any battery acid or corrosive residue on the battery. Using your bare hands to change a battery is NOT a good idea because battery acid can cause nasty and painful burns. If you do get battery acid on your hands, flush immediately with lots of water and/or neutralize the acid with baking soda.

Remove the battery buy lifting it up and out of the battery tray or compartment. If the battery does not have a strap on top to make lifting easier, you can use a battery carrying tool to grasp the battery and lift it out.

Keep the battery upright because acid may spill out of the caps or vents on top if the battery is tilted or upset. This is NOT a concern with AGM batteries because they have no liquid inside to spill.

Inspect the condition of the tray under the battery. If your vehicle has a steel tray and the tray is badly corroded replace it. Plastic battery trays are best because they will not rust or corrode. Make sure the battery tray is firmly attached and is capable of supporting the weight of the battery.

Inspect and clean the clamps on the ends of the battery cables. Replace the cables if they are loose, severely corroded or damaged. Use good quality replacement cables that have the proper gauge wire inside to assure adequate amp flow for starting and charging.


Before you install your new battery, test its charge level with a digital voltmeter.

A fully charged battery should read 12.6 to 12.7 volts. If the voltage reading is low, put the battery on a charger to bring it back up to full charge BEFORE you install it in your vehicle. Batteries come precharged from the factory, but can slowly loose their charge if they have sat for many months on a store shelf.

Place the new battery on the tray, install the base clamp or battery strap and tighten as needed to secure the battery. This is very important to prevent the battery from bouncing around while you are driving. Excessive vibration can damage a battery very quickly, and there is a danger of the battery shorting out if it moves around and the positive post or cable comes into contact with anything metal.

clean battery posts

Use a battery post cleaning tool to clean the battery posts and the inside surfaces of both clamps on the battery cables. You want a nice, bright clean surface to assure good electrical contact. Even a tiny film of oxide on the surface can create resistance that may cause starting and charging problems.

Install the positive battery cable first, then the negative. Tighten the clamps but be careful not to over tighten and damage the clamps.

Apply a thin coating of chassis grease to the clamps and posts to help protect them from moisture and corrosion. Or, before you install the battery cables, install felt anti-corrosion washers on each post. The washers are chemically treated to prevent corrosion.

Finally, double-check all of your connections, make sure the battery holddown strap or clamp is secure and that both battery cables are clean and tight. The start your engine to make sure the battery is delivering normal power to the starter motor.

If your vehicle does not crank, clean and retighten both battery cables. Also check the other ends of the cables where they connect to chassis ground and the power center or wiring harness to make sure the others ends are clean and tight.

Still won't crank? Then you have a starter circuit problem that will require further diagnosis. See STARTER DIAGNOSIS or ENGINE WON'T START for more information.

Your Vehicle May Require a "Battery Reset"

IMPORTANT NOTE: On many some late model vehicles, there is an additional step that is required AFTER installing a new battery. You have to tell the PCM that a new battery has been installed using a professional grade bi-directional scan tool or special battery reset tool. A simple DIY OBD scan tool can't do this! A battery reset is necessary because the PCM also controls the charging system and the voltage at which the battery is charged. A new battery requires a different charging rate than an old battery. So telling the PCM that the battery has been replaced allows it to reset its charging schedule for a new battery. If this step is NOT done, the PCM may not maintain the battery's state of charge adequately, causing it run down and fail prematurely.

Bartec USA has a special tool called a "OST200 Battery Management Reset Tool" that can perform the required battery reset in about 30 seconds on late model vehicles.


Most stores that sell batteries require charge a core fee ($12 to $18) to encourage people to recycle their old car batteries.

You will get the core deposit back when you return your old battery for recycling.

book More Car Battery Articles:

Car Battery Safety & Jump Starting (Read First!!!)

Car Battery Disconnect Problems (Read This BEFORE Disconnecting or Replacing Your Battery)

Diagnose a Battery that Keeps Running Down

Battery FAQs

Hybrid Safety Hazards

Car Battery Testing

Starting & Charging System Troubleshooting

Charging System Checks (alternator testing)

Diagnosing An Engine that Won't Crank or Start

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