by William Darden
CAR BATTERY FREQUENTLY ASKED QUESTIONS
JUNE 24, 1995
A word of caution. Batteries contain a sulfuric acid electrolyte which is a highly corrosive poison and produces gasses that will explode if ignited. When working with batteries, you need to remove jewelry, wear protective clothing and eye ware, and exercise caution. Follow the manufacturer's instructions for testing, jumping, installing and charging.
1. WHAT IS THE BOTTOM LINE? A. Check specific gravity in each cell and remove surface charge before load testing, B. Retest after deep discharges or jump starts, C. Recharge slowly at 14.6 volts, D. Buy the freshest and largest Reserve Capacity, non-sealed (low maintenance) car battery that will fit with a CCA rating for your climate that meets or exceeds the car's OEM cranking amps requirements, and E. Perform preventative maintenance, especially during warm weather. 2. WHY BOTHER? Because only the rich can afford cheap batteries..... A good quality car battery will cost between $50 and $100 and, if properly maintained, will give you four to eight years of service. The purpose of a battery is to start the car; to provide power for the ignition, lighting and other accessories when their combined load exceeds the capability of the alternator; and to filter the power. Dead batteries almost always occur at the most inopportune times, e.g., returning home from a long trip, during bad weather, late at night in a dark parking lot or when you are late for an appointment. You can easily spend the cost of a new battery or more for an emergency jump start or tow. Most store employees do not know how to correctly test a battery. The national average of "defective" batteries returned to the manufacturer that are in fact good is 50%. 3. HOW DO I TEST A BATTERY? A. Visually inspect for obvious problems, e.g., damaged case, corrosion, loose hold-down clamps or cable terminals, or low electrolyte. B. If you have just recharged you battery or driven your car, eliminate any surface charge by one of the following methods; otherwise, go to the next step: 1. Allow the battery to sit for two to three hours, 2. Turn the headlights on high beam for three minutes and wait five minutes before further testing, or 3. With a battery load tester, apply a 150 amp load for 10-15 seconds. C. Using the following table, determine the battery's state-of-charge. The BEST way to measure the state-of-charge is to check the specific gravity in each cell with a hydrometer. A temperature compensating hydrometer can be purchased at a auto parts store for approximately five dollars. If the battery is sealed (maintenance free), the correct procedure to test it is to measure the battery's voltage WITHOUT the engine running with a good quality digital DC voltmeter. Some sealed batteries have built-in hydrometers. They are not good testing devices because they only measure the state-of-charge in one of the six cells. If the state-of-charge is BELOW 75% using either test, then the battery needs to be recharged BEFORE proceeding. If there is a .050 or more difference in the specific gravity reading between the highest and lowest cell or the battery will not recharge to 75% or higher, then the battery should be replaced. Battery Approximate Average Cell Voltage State-of-charge Specific Gravity 12.66 100% 1.265 12.45 75% 1.225 12.24 50% 1.190 12.06 25% 1.155 11.89 0% 1.120 Note: If the temperature of the electrolyte is below 70 degrees F, then add .012 volts (12 millivolts) per degree below 70 degrees F. D. If the battery's state-of-charge is at 75% or higher, then load test the battery by one of the following methods: 1. Turn the headlights on high beam for six minutes, 2. Disable the ignition and turn the engine over for 15 seconds with the starter motor, 3. With a battery load tester, apply a load equal to one half of the Cold Cranking Amp (CCA) rating of the battery, or 4. With a battery load tester, apply a load equal to one half the Original Equipment Manufacturer (OEM) cranking amp specification. DURING the load test, the voltage on a good battery will NOT drop below 9.7 volts with the electrolyte at 80 degrees F. (If the electrolyte is above 80 degrees, add .1 volt for every 10 degrees above 80 until you reach 100 degrees. If below 80 degrees, subtract .1 volt for every 10 degrees until 40 degrees.) After the load is removed, the battery should "bounce back" to the 50% state-of-charge level or above. If the battery drops below minimum test voltage, does not bounce back or will not start the engine, then you should replace it. If it passes this test, you should recharge your battery to restore it to peak performance. 4. HOW DO I KNOW IF MY CHARGING SYSTEM IS OK? When the charging system fails, usually the alternator light will come on. With a good battery and the engine running at 2000 RPM or more for two minutes, depending on the load and ambient temperature, the voltage will increase to between 13.0 and 15.1 volts. Other factors affecting the charging voltage are the battery's age, state of charge, and electrolyte level and purity. A loose alternator belt will significantly reduce the alternator's output. 5. HOW DO I JUMP START MY CAR? This assumes a 12 volt negative grounded system found on almost every car in the United States. A. Determine that the electrolyte is NOT frozen. If frozen, allow to thaw. B. Turn off all unnecessary accessories and lights on both cars. C. Start the car with the good battery and let it run for at least two or three minutes at fast idle BEFORE attempting to start the disabled car. D. Connect the POSITIVE terminal on the disabled battery to the POSITIVE terminal on the good battery. E. Connect the NEGATIVE terminal on the good battery to a clean, unpainted area on the ENGINE BLOCK on the disabled car. F. Let the good car to continue to run for five minutes or more. This will allow the dead battery to receive some charge and to warm it's electrolyte. G. Start the disabled car and allow to run at fast idle. H. Disconnect the jumper cables in the reverse order, starting with the ENGINE BLOCK on the disable car. 6. WHAT DO I LOOK FOR IN BUYING A NEW BATTERY? A. Cold Cranking Amps The most important consideration is the battery's CCA rating. CCAs are the discharge load measured in amps that a fully charged battery at 0 degrees F can deliver for 30 seconds and while maintaining the voltage above 7.2 volts. Batteries are sometimes advertised by their Cranking Amps (CA) measured at 32 degrees or Hot Cranking Amps (HCA) measured at 80 degrees, which are not the same as CCA. Do not be mislead by CAs or HCAs. To convert CAs to CCAs, multiply the CAs by .8. To convert HCAs to CCAs, multiply HCAs by .69. In hot climates, buying batteries with double or triple the CCA ratings that exceed the OEM requirement is a WASTE of money. However, in colder climates the higher CCA rating the better, due to increased power required to crank a sluggish engine and the inefficiency of the cold battery. One of the major manufacturers, Exide, publishes the following table: Available Power Temperature Power Required From Battery degrees F To Crank Engine 100% 80 100% 65% 32 155% 40% 0 210% 25% -32 350% B. Reserve Capacity The next most important consideration in buying a battery is the Reserve Capacity (RC) rating because of the effects of an increased parasitic or "key off" load produced by electrical devices, e.g., fans, clocks, computers, etc., that operate after the engine is stopped. RC is the number of minutes a fully charged battery at 80 degrees F can be discharged at 25 amps until the voltage falls below 10.5 volts. More RC is better in every case. For example, if your car has a 360 OEM cranking amp requirement, then a 450 to 500 CCA rated battery with 120 minute RC would be more desirable in a warm climate than one with 700 to 800 CCA with 90 minutes of RC. C. Type A sealed or "maintenance free" battery will NOT allow you to test the specific gravity with a hydrometer or add DISTILLED water when required. Sealed batteries are more prone to deep discharge failures, but require less preventative maintenance. Car batteries are specially designed for high initial cranking amps (usually for five seconds) to start a car; whereas, deep cycle or "marine" batteries are designed for prolonged discharges at lower amperage. A "dual marine" battery is a compromise between a car and deep cycle battery. However, a CAR battery will give you the best performance in a car. Some manufactures have introduced a "dual" battery that combines a standard battery with emergency backup cells. For about the same cost a better approach is to buy two batteries and isolate them. D. Size Manufacturers build their batteries to an internationally adopted BCI group number (24F, 35, etc.) specification, which is based on the physical case size, terminal placement and terminal polarity. The OEM battery group number is a good starting place to determine the replacement group. Within a group, the CCA and RC ratings, warranty and battery type will vary in models of the same brand or from brand to brand. Batteries are generally sold by model, so the group numbers will vary for the same price. This means that for the SAME price you can potentially buy a physically larger battery with more RC than the battery you are replacing. Be sure that the replacement battery will fit, the cables will correct to the correct terminal, and that the terminals will NOT touch the hood when closed. The battery manufacturers publish application guides that will contain the OEM cranking amp and group number replacement recommendations by make, model and year of car, and battery size, CCA and RC specifications. Manufacturers might not build or the store might not carry all the group numbers. To reduce inventory costs, dual terminal "universal" batteries that will replace several group sizes are becoming more popular. The four largest domestic battery manufacturers are Johnson Controls (Interstate, Motorcraft, Energizer, older Diehards), Delco (Sears, newer Diehards), GNB (Champion) and Exide (NAPA). E. Freshness Determining the "freshness" of a battery is sometimes difficult. NEVER buy a battery that is MORE than SIX months old. The date of manufacture is stamped on the case or printed on a sticker. It is usually a combination of alpha and numeric characters with letters for the months starting with "A" for January (skipping "I") and digit for the year, e.g., "F5" for June, 1995. Like bread, fresher is definitely better. F. Warranty As with tire warranties, battery warranties are not necessarily indicative of the quality or cost over the life of the car. Manufacturers will prorate warranties based on the LIST price, so if a battery failed half way or more through its warranty period, buying a NEW replacement might cost you less. The exception is the free replacement warranty period. This represents the risk that the manufacturer is willing to assume. A longer free replacement warranty period is better. 7. HOW DO I INSTALL A BATTERY? A. Thoroughly wash and clean the old battery, battery terminals and case or tray with water to minimize problems from acid or corrosion. Heavy corrosion can be neutralized with a mixture of baking soda and water. Auto parts stores sell a cheap wire brush that will allow you to clean the inside of a terminal clamps. Mark the positive cable so you do not forget which one it is when you reconnect. B. Remove the NEGATIVE cable first, the POSITIVE cable and then the hold-down bracket or clamp. Dispose the old battery by exchanging it when you buy your new one or at a recycling center. Batteries contain large amounts of lead and acid. C. After removing the old battery, be sure that the battery tray and cable connectors are clean. If the cables are corroded or damaged, replace them; otherwise, they will significantly reduce starting capability. D. Place the replacement battery so that the NEGATIVE cable will connect to the NEGATIVE terminal. Reversing the polarity of the electrical system WILL severely damage it. E. After replacing the hold-down bracket, reconnect the POSITIVE cable first and then the NEGATIVE cable. F. Before starting the engine, check the electrolyte levels and state-of-charge and refill or recharge as required. G. Coat the terminals with a high temperature grease to prevent corrosion. If you do not want to lose your car's computer memory, security codes or radio settings, a second battery can be temporarily connected to the electrical system in parallel before disconnecting the first one. A cigarette lighter plug can easily connect a parallel battery. 8. HOW DO I CHARGE MY BATTERY? Some more words of caution. Do NOT ever disconnect a battery cable from car with the engine running because the battery acts like a filter for the electrical system. Unfiltered electricity can damage the electrical components, for example, computer, radio, etc. Check the electrolyte level before recharging. Do NOT add water if the electrolyte is covering the top of the plates because during the recharging process, it will warm up and expand. After recharging has been completed and the electrolyte has cooled, RECHECK the level and add DISTILLED water to 1/8" BELOW the bottom of the filler tube (vent wells) or to the level indicated by the battery manufacturer. Reinstall the vent caps before recharging and recharge ONLY in well ventilated areas. NO smoking, sparks or open flames because while being recharged, batteries give off explosive gasses. If your battery is the sealed, do NOT recharge with high current. A. Usually, a car is jump started and run to recharge the battery, which might NOT fully charge it. The length of time to fully recharge the battery depends on the amount of discharge, the amount of surplus current that is diverted to the battery, how long the engine is run, RPM, and temperature. That is, an alternator is sized by the car manufacturer to carry the maximum accessory load and maintain a battery, NOT recharge a dead one. If you jump start your car, test your battery after you have finished driving it, and recharge if the state-of-charge is below 75%. B. A better method to recharge batteries is to use an external constant current charger which is set not to deliver more than 1% of the CCA rating of the battery. C. The best method is to use an external constant voltage or tapered current charger. A constant voltage "automatic" charger applies regulated voltage at approximately 14.6 volts. A 10 amp automatic charger will cost between $30 and $50 at an auto parts store. To prevent damage to the battery, the current should be less than 1% of the CCA rating during the first 30 minutes. With a taper charger, a high current, up to 30 amps, is applied to the battery for a short period up to 30 minutes maximum and then is regulated downward until the charge state reaches 100%. For batteries with a state-of-charge of 25%, the following table, published by Interstate Batteries, lists the recommended battery charging rates and times: Reserve Capacity Slow Charge Fast Charge (RC) Rating @ 5 Amps @ 20 Amps 80 Minutes or less 10 Hours 2.5 Hours 80 to 125 Minutes 15 Hours 4 Hours 125 to 170 Minutes 22 Hours 5 Hours If left unattended, cheap, unregulated trickle battery chargers can overcharge your battery, because they can "boil off" the electrolyte. Do NOT use fast, high rate, or boost chargers on any battery that is sulfated or deeply discharged. This condition requires a constant current from one to two amps for 60 to 100 hours. The electrolyte should NEVER bubble violently while recharging. High currents only create heat and excess gas. 9. CAN I INCREASE THE LIFE OF MY BATTERY? Keeping your battery well maintained is the BEST way to extend the life of your battery. For cold climates, keeping the battery fully charged and warm will help. In the warmer climates and during the summer, the electrolyte levels need to be checked more frequently and DISTILLED water added, if required. Batteries last approximately two thirds as long in hot climates as cold ones. The parasitic load will determine how long a car can sit and still be started. Disconnecting the NEGATIVE cable will extend the "life" of the battery. Turning off unnecessary accessories and lights BEFORE starting your car will decrease the load on the battery while cranking. Leaving your lights on and fully discharging the battery can ruin it, especially if it is the sealed or maintenance free type. Should this occur, you should test the battery after it has been recharged to determine if there is permanent damage. NEVER add acid or additives--just water. Maintaining the correct electrolyte levels, tightening loose hold-down clamps and terminals, and removing corrosion is normally the ONLY preventative maintenance required for a battery. 10. WHAT ARE THE MOST COMMON CAUSES OF BATTERY FAILURES? A. Using an undersized battery, B. Loss of electrolyte due to heat or overcharging, C. Overcharging with voltages greater than 15.1 volts, D. Undercharging, E. Old age, F. Vibration, G. Deep discharges (leaving your lights on), H. Using tap water, I. Corrosion, J. Freezing, and K. Overheating. 11. WHAT ARE SOME OF THE MYTHS ABOUT BATTERIES? A. Storing a battery on a concrete floor will discharge them. Modern lead acid battery cases are better sealed, so external leakage causing discharge is no longer a problem. B. Driving a car will fully recharge a battery. There are a number of factors affecting alternator's ability to charge a battery. The greatest factors are how much current from the alternator is diverted to the battery to charge it, how long the current is available and temperature. Generally, short trips during bad weather will not recharge the battery; whereas, a long daytime drive in good weather will. C. A battery will not explode. While recharging, a battery produces hydrogen and oxygen gasses. If a spark occurs, an explosion can occur. Remember the "Hindenburg"! D. A battery will not lose it's charge sitting in storage. A battery has internal electrical leakage that will cause it to become fully discharged and sulfated over time. Prior to storing a battery, it should be fully charged and recharged when it reaches the 50% state-of-charge level. Batteries on store shelves should be checked periodically and recharged if necessary. E. Maintenance free battery never requires electrolyte. In warm climates, the electrolyte could be "boiled off" due to the high underhood temperatures. It could also be lost due to excessive charging voltage or using high charging currents.