The following document is here with the permission of it's author, Bill Darden. Bill's deep cycle battery faq is also available at this site.

Information posted here is to be used at your own risk,as all of the usual disclaimers apply.

January 1, 2001

A word of caution. Batteries contain a sulfuric acid electrolyte, which is a highly corrosive poison and will produce gases when re charged and explode if ignited. This will hurt you--BAD! When working with batteries, you need to have plenty of ventilation, remove your jewelry, wear protective clothing and eye wear (safety glasses), and exercise extreme caution. Whenever possible, please follow the battery manufacturer's instructions for testing, jumping, installing and charging. This FAQ assumes a 12 volt negative grounded battery found in most cars, light trucks and vans in North America with apologies to international readers.

The technical stuff is in [brackets].



At the first sign of slow starting, headlights dim at idle, gauges indicate discharge with engine running at high idle, or your battery seems to be losing performance, recharge, remove the surface charge, and load test it! (See Section 4.)

B. Perform regular preventive maintenance, especially during HOT weather and before COLD weather, (See Section 3)

In hot climates, use non-sealed batteries. (See Section 7)

D. Keep the battery charged, but do NOT overcharge, (See Section 9)

E. Buy the freshest and largest Reserve Capacity (RC), battery that will physically fit with a Cold Cranking Amp (CCA) rating for your climate that meets or exceeds the car's Original Equipment Manufacturer's (OEM) cranking amp requirement, and (See Section 7)

F. After deep discharges or jump starts, recharge, remove the surface charge and load test batteries for latent damage. (See Section 4)


Because only the rich can afford cheap batteries.....

A good quality battery will cost between $50 and $100 and, if properly maintained, it should last an average of five years. The primary purpose of a car battery is to START the engine. Its secondary function is to filter or stabilize the power. It also provides extra power for the ignition, lighting, sound system and other accessories when their combined load EXCEEDS the capability of the charging system. Finally, a car battery provides a source of power to the electrical system when the charging system is not operating.

A battery "ages" as the active plate material sheds (or flakes off) due to the normal expansion and contraction that occurs during the discharge and recharge cycles or sulfate coats the plates. Deep discharges, heat, vibration or non-use accelerate this "aging" process. Sediment [mud] builds up and the can short the cell out. Another major cause of premature battery failure is sulfation. When batteries are stored over three months, lead sulfate makes the plates very hard and dense and the battery less capable or unable to be recharged. When the active material in the plates can no longer sustain a discharge current and the battery "dies". In a hot climate, the harshest environment for a battery, a Johnson Controls Inc. survey of junk batteries revealed that the AVERAGE life of a good quality car battery was 37 months.

If your battery is more than five years old, then it is living on borrowed time. Slow cranking, especially on a cold day, is another good indication that your battery is going bad and it should be externally recharged and load tested. Dead batteries almost always occur at the most inopportune times, for example, AFTER you have jump started your car, at the airport 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 of the "defective" batteries returned to the manufacturer during free replacement warranty periods are good. This suggests that some SELLERS of new batteries do not know how or take the time to properly load test or recharge batteries.


Maintaining the correct electrolyte levels, tightening loose hold-down clamps and terminals, removing corrosion, and checking the alternator belt tension is normally the ONLY preventive maintenance required for a battery. The preventive maintenance frequency is dependent upon climate and battery type, but you should perform at least once before cold weather starts and once a month in hot weather.

If the electrolyte levels are low in non-sealed batteries, add DISTILLED water to the level indicated by the battery manufacturer or to 1/8 inch BELOW the bottom of the filler tube (vent wells). The plates need to be covered and avoid OVERFILLING, especially in hot climates, because the heat will cause the electrolyte to expand and overflow.


There are six simple steps to test a car battery--inspect, recharge, remove surface charge, load test, and recharge. To test a battery (or to troubleshoot charging or electrical systems), you will need a digital voltmeter with .5% or better accuracy. A digital voltmeter can be purchased at an electronics store, for example, Radio Shack, for between $20 and $200. If you have a non-sealed battery, it is highly recommended that you use a temperature compensating hydrometer which can be purchased at an auto parts store between $5 and $20. A hydrometer is a very accurate way of determining a battery's state-of-charge and weak or dead cells.


Visually inspect for obvious problems, e.g., loose alternator belt, low electrolyte, corroded cables or terminal clamps, loose hold-down clamps, loose cable terminals, or a damaged battery case.


Using a charger, recharge [equalize] the battery to 100% state-of-charge. See Section 9 on recharging.


If you have just externally recharged your battery or driven your car, you can eliminate any surface charge by one of the following methods; otherwise, go to the Step D:


Without the engine running, measure the battery and use the following table [calibrated at 70 degrees F] to determine the battery's state-of-charge:

State of Charge Specific Gravity Data
Open Circuit
Battery Voltage
Average Cell
Specific Gravity
12.65+ 100% 1.265+
12.45 75% 1.225
12.24 50% 1.190
12.06 25% 1.155
11.89 0% 1.120

[If the temperature of the electrolyte is BELOW 70 degrees F, then SUBTRACT .12 volts (120 millivolts) per 10 degrees below 70 degrees F to the Open Circuit Battery Voltage reading in the above table. For example, at 32 degrees F the Open Circuit Terminal Voltage at 100% state-of-charge would be 12.19 VDC. If the temperature of the electrolyte is ABOVE 70 degrees F, then ADD .12 volts (120 millivolts) per 10 degrees below 70 degrees F to the Open Circuit Battery Voltage reading in the above table. For example, at 100 degrees F the Open Circuit Terminal Voltage at 100% state-of-charge would be 13.01 VDC.]

For non-sealed batteries, check the specific gravity in each cell with an external hydrometer. For sealed batteries, measure the voltage across the battery terminals with an accurate digital voltmeter. It is the only way you can determine the state-of-charge. Some batteries have a built-in hydrometer which only measures the state-of-charge in ONE of its six cells. If the built-in indicator is clear or light yellow, then the battery has a low electrolyte level and should be refilled before proceeding, If sealed, the battery should be replaced.

If the state-of-charge is BELOW 75% using either the specific gravity or voltage test or the built-in hydrometer indicates "bad" (usually dark), then the battery needs to be recharged BEFORE proceeding. Replace the battery, if one or more of the following conditions occur:


If the battery's state-of-charge is at 75% or higher or has a "good" built-in hydrometer indication, then load test the battery by one of the following methods:


Your car's charging system is composed of an alternator [or DC generator], a voltage regulator, battery and indicator light or gauge. While your engine is running, the charging system's primary purpose is to provide power for the car's electrical load, for example, ignition, lighting, audio system, accessories, etc., and to recharge your car's battery.

When the charging system fails, usually an indicator light will come on or the voltage gauge will not register "good". The most common charging system failure is a loose, worn or broken alternator belt, so check it first. If OK, then with a known good battery and the engine running at 2000 RPM or more for two minutes, depending on the load and ambient temperature, the voltage should increase to between 13.0 and 15.1 volts. Most cars will measure between 14.0 and 14.8 volts on a warm day, depending on the battery type that the charging system was designed for.

[Most voltage regulators are temperature compensated to properly charge the battery under different environmental conditions. As the ambient temperature decreases, the charging voltage is increased to overcome the higher battery resistance. Conversely, as the ambient temperature increases, the charging voltage is reduced. Other factors affecting the charging voltage are the battery's condition, state-of-charge, electrical load and electrolyte purity.]

If terminal voltage is below 13.0 volts and the battery tests good after being externally recharged or if you are still having problems keeping it charged, then have the charging system's output voltage and current and car's parasitic (key off) load tested. A loose alternator belt or bad diode will significantly reduce the alternator's current output.

If output voltage is above 15.1 volts with the ambient temperature above freezing, the battery's electrolyte level is frequently low, or you smell "rotten eggs" around the battery, then you are probably overcharging the battery and the charging system should be tested.


In cold weather, a good quality booster cable with six gauge (or less) wire is necessary to provide enough current to the disabled car to start the engine. [The smaller the wire gauge number, that is, the larger the wire diameter, the better.] Please check the owner's manual for BOTH vehicles BEFORE attempting to jump start. Follow the manufacturer's procedure because some good cars should not be running during a jump start of a disabled one. However, starting the disabled car with the good car running, can prevent having both cars disabled. AVOID the booster cable clamps touching each other or the POSITIVE clamp to touch the frame or engine block.


Battery buying strategy for use in Canada, for example, is different than hot climates that you find in Texas. In the colder climates, higher CCA ratings are more important; whereas, in a hot climate, a higher RC ratings are more important once the CCA rating has satisfied the OEM cranking amp requirement.

A. Cold Cranking Amps (CCA)

The most important consideration is sizing the battery's CCA rating to MEET OR EXCEED, depending on the climate, the car's OEM cranking requirement. [CCAs are the discharge load measured in amps that a fully charged battery at 0 degrees F (-17.8 degrees C) can deliver for 30 seconds and while maintaining the voltage above 7.2 volts. Batteries are sometimes advertised by their Cranking Performance Amps (CA) or Marine Cranking Amps (MCA) measured at 32 degrees F (0 degrees C) or Hot Cranking Amps (HCA) measured at 80 degrees F (26.7 degrees C), which are not the same as CCA. Do not be mislead by CA, MCA or HCA ratings. 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. As batteries age, they are less capable of producing CCAs.

One of the major battery manufacturers, Exide, publishes the following table:

Exide Power vs. Temperature Data
Available Power
From Battery
degrees F
Power Required
To Crank Engine
100% 80 100%
65% 32 155%
40% 0 210%
25% -32 350%

[If more CCA capacity is required, two (or more) 12 volt batteries can be connected in parallel. Within a BCI group size, generally the battery with more CCA will have more plates because a larger surface area is required to produce the higher current.]

B. Reserve Capacity (RC)

The second most important consideration is the Reserve Capacity rating because of the effects of an increased parasitic (key off) load and in emergencies. [RC is the number of minutes a fully charged battery at 80 degrees F (26.7 degrees C) can be discharged at 25 amps until the voltage falls below 10.5 volts.] More RC is better in every case! In a hot climate, for example, if your car has a 360 OEM cranking amp requirement, then a 400 CCA rated battery with 120 minute RC with more electrolyte would be more desirable than one with 1000 CCA with 90 minutes of RC.

[If more RC is required, two six volt batteries can be connected in series or two (or more) 12 volt batteries can be connected in parallel. Within a BCI group size, generally the battery with larger RC will weigh more because it contains more lead.]

C. Type

The two most common types of CAR batteries are low maintenance (non-sealed) and maintenance free (non-sealed or sealed). [The low maintenance batteries have a lead-antimony/calcium (dual alloy or hybrid) plate formulation. Maintenance free batteries have a lead-calcium/calcium formulation.] The advantages of maintenance free batteries are less preventive maintenance, longer life, faster recharging, greater overcharge resistance, reduced terminal corrosion and longer shelf life. The disadvantages are that they are more prone to premature failures due to deep discharges. In hot climates, buying non-sealed maintenance free batteries is recommended because a sealed maintenance free battery will NOT allow you to replace the water when required. If you replace a sealed maintenance free battery in a GM car, for example, with a non-sealed lead-antimony or lead-antimony/calcium low maintenance battery, you will need to check the electrolyte levels more often. This is because GM sets their voltage regulators at 14.8 volts for the sealed maintenance free lead-calcium/calcium batteries, like the OEM AC Delco batteries.

Some manufacturers introduced a "dual" battery, that combines a standard battery with switchable emergency backup cells. For about the same cost a better approach would be to buy two batteries and isolate them. Sears DieHard Security, have been introduced for Approximately $170. When it is switched off it will not allow the engine to be started, but will provide power for the parasitic or "key off" load. Consumer Reports has tested it and indicates that the security feature can be defeated in less than one minute.

In the future, you can expect to see more expensive absorbed glass mat (AGM) batteries in the $100 to $150 price ranges. Examples of AGM batteries are Optima, Interstate's Extreme Performance, Concorde's Lifeline, Exide, AC Delco's Platinum, and Champion's Vortex. This is because car manufacturers want to extend their "bumper-to-bumper" warranty periods, to relocate the battery from under the hood to avoid temperature extremes, or to save under hood space. The advantages of AGM batteries are they are maintenance free without the disadvantages and they will last three to five times longer. [Expect to see 36 volt AGM car batteries with 14/42 volt dual or 42 volt electrical systems introduced in the next five years.]

For off road applications in trucks, recreational vehicles (RVs), 4x4s, vans or sport utility vehicles, some manufacturer's distribute "high vibration" or RV battery versions designed to reduce the effects of moderate vibration. For excessive vibration applications, it is best to buy a commercial or AGM battery.

Car batteries are specially designed for high initial cranking amps (usually for five to 15 seconds) to start an engine; 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. A deep cycle or "dual marine" battery will work as car battery if it can produce enough CCA to start the engine. For RV's, a car battery is normally used to start the engine and a deep cycle battery is used to power the RV accessories. The batteries are connected to a diode isolator and both are automatically recharged by the RV's charging system when engine is running. An excellent and easy to understand free booklet on multi-battery applications can be obtained from the Sure Power Introduction to Batteries and Charging Systems (PDF File) or by calling (800) 845-6269 or (503) 692-5360 and requesting the "Introduction to Batteries and Charging Systems" written by Ralph Scheidler.

D. Size

Manufacturers build their batteries to an internationally adopted Battery Council International (BCI) group number (24, 26, 70, 75, 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, e.g. a 34/78 group might replace a smaller 26/70 group and give you an additional 30 minutes of RC. If you do this, be sure that the replacement battery will fit, the cables will connect to the correct terminals, and that the terminals will NOT touch the hood when closed.

BCI and the battery manufacturers publish application guides that will contain the OEM cranking amperage requirements 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 BCI group numbers. To reduce inventory costs, dual terminal "universal" batteries that will replace several group sizes are becoming more popular and fit 75% or more of cars on the road today.

Battery manufacturers or distributors will often "private label" their batteries for large chain stores. Below is a list in alphabetical order of the largest battery manufacturers/distributors in North America and some of their brand names, trademarks and private labels. Ownership, branding, Web addresses and telephone numbers are subject to change. For example. Exide recently purchased GNB.

  1. Delphi Automotive

  2. Concorde (

  3. Crown (

  4. Douglas (800-368-4527 or

  5. East Penn (610-682-6361 or

  6. Exide (800-782-7848 or

  7. GNB (800-242-6750 or

  8. Hawker Energy Products (

  9. Johnson Controls Inc. ( and

  10. New Castle (724-658-5501 or

  11. Optima (

  12. Superior (

E. Freshness

Determining the "freshness" of a battery is sometimes difficult. NEVER buy a battery that is MORE than SIX months old because it is starting to sulfate. [Sulfation occurs when lead sulfate can not be converted back to charged material and is created when discharged batteries stand for a long time or from excessive water loss.] 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 (generally skipping the letter "I") and digit for the year, e.g., "J6" for September, 1996. 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. Most manufacturers will prorate warranties based on the LIST price of the bad and replacement battery, so if a battery failed half way or more through its warranty period, buying a NEW battery outright might cost you less than paying the difference under a prorated warranty. The exception to this 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 and is usually an indication of the quality of the battery.


A car battery weights between 30 and 60 pounds, so the first question is do I want to install it myself? The second question is what do I do with the old battery if not exchanged for the new one? Insure that you have your radio and security codes before disconnecting the old battery. [A second battery can be temporarily connected to the electrical system in parallel before disconnecting the first one. If active when the key is off, a cigarette lighter plug can used to easily connect a parallel 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. Also, mark the cables so you do not forget which one it is which when you reconnect.

B. Remove the NEGATIVE cable first because this will minimize the possibility of shorting the battery when you remove the other cable. Next remove the POSITIVE cable and then the hold-down bracket or clamp. If the hold down bracket is severely corroded, replace it. Dispose the old battery by exchanging it when you buy your new one or by taking it to a recycling center. Please remember that batteries contain large amounts of harmful lead and acid.

C. After removing the old battery, insure that the battery tray, cable terminals, and connectors are clean. Auto parts stores sell an inexpensive wire brush that will allow clean the inside of a terminal clamps and the terminals. If the terminals, cables or hold down brackets are severely corroded, replace them. Corroded terminals or cables will significantly reduce your starting capability because of their inability to carry the high current required.

D. Thinly coat the terminal and terminal clamps with a high temperature grease or petroleum jelly (Vaseline) or to prevent corrosion. Red and green felt battery post corrosion preventors or battery pads found at most auto parts stores may also be used.

E. 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 or DESTROY it or cause the battery to explode.

F. After replacing the hold-down bracket, reconnect the cables in reverse order, that is, attach the POSITIVE cable first and then the NEGATIVE cable last. Do NOT over tighten the General Motors type side battery post terminals or you could crack the battery case.

G. Before starting the engine, check the electrolyte levels and state-of-charge. Refill or recharge as required.


In addition to the earlier cautions, some more words of caution:

A. NEVER, NEVER disconnect a battery cable from car with the engine running because the battery acts like a filter for the electrical system. Unfiltered [pulsating DC] electricity can damage expensive electrical components, e.g., computer, radio, charging system, etc.

B. Check the electrolyte level and be sure it is not frozen BEFORE recharging.

C. Avoid adding distilled 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 battery has cooled, RECHECK the levels.

D. Reinstall the vent caps BEFORE recharging, recharge ONLY in well ventilated areas, and wear protective eye wear. NO smoking, sparks or open flames because while the battery is being recharged because they give off explosive gasses.

E. If your battery is sealed, avoid recharging with current ABOVE 25 amps.

F. Follow the battery and charger manufacturer's procedures for connecting and disconnecting cables and operation to minimize the possibility of an explosion or incorrectly charging the battery. Generally you should turn the charger OFF before connecting or disconnecting cables to a battery.

G. If a battery becomes hot, or if violent gassing or spewing of electrolyte occurs, turn the charger off temporarily or reduce the charging rate.

H. Insure that in car charging with an external charger will not damage the car's electrical system with high voltages. If this is even a remote possibility, then disconnect the car's negative battery cable from the battery BEFORE connecting the charger.

Usually, when car is jump started, it is driven to recharge [or equalize] the battery. This 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, engine speed, and ambient temperature. That is, an alternator is sized by the car manufacturer to carry the maximum accessory load and to maintain a battery and NOT to recharge a dead one.

[For example, if 300 amps are consumed for ten seconds to start a car from a fully charged battery, it will take the charging system approximately two and one half minutes to replace the power used. If 25 amps are available to recharge the battery, it will take six minutes at ten amps or an hour at one amp. Using the same example with a dead 120 minute RC battery, it would take approximately 86 times longer to recharge it or three and one half hours at 25 amps, 8.7 hours at 10 amps, or 86.4 hours at one amp].

If you have added lights, audio amplifiers, winches or other high powered accessories and engage in "stop-and-go driving, the alternator might NOT produce enough current to keep your battery fully charged. You might need to increase the capacity of the charging system. [Ideally the combined load of all the accessories should be less than 75% of the charging system's maximum output, so that at least 25% is available to recharge the battery.]

A better method to recharge batteries is to use an external constant current charger which is set not to deliver more than 12% of the RC rating of the battery and monitor the state-of-charge. For fully discharged batteries, the following table, published by BCI, lists the recommended battery charging rates and times:

BCI Charge Rate vs. Time Data
Reserve Capacity
(RC) Rating
Slow Charge Fast Charge
80 Minutes or less 15 Hours @ 3 amps 2.5 Hours @ 20 amps
80 to 125 Minutes 21 Hours @ 4 amps 3.75 Hours @ 20 amps
125 to 170 Minutes 22 Hours @ 5 amps 5 Hours @ 20 amps
170 to 250 Minutes 23 Hours @ 6 amps 7.5 Hours @ 20 amps
Above 250 Minutes 24 Hours @ 10 amps 6 Hours @ 40 amps

The BEST method is to SLOWLY recharge it using an external constant voltage (or tapered current charger) because the electrolyte has more time to penetrate the plates. A constant voltage or "automatic" charger applies regulated voltage at approximately 14.6 volts at 70 degree F. An automatic 10 amp charger will cost between $30 and $60 at an auto parts store. [To prevent damage to a fully discharged 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, can be applied to non-sealed batteries for a short period up to 30 minutes maximum and then is regulated downward until the charge state reaches 100%. An excellent automatic constant voltage battery charger is a 15 volt regulated power supply adjusted to 14.58 volts at 70 degrees F. If 32 degrees F, then increase the charging voltage to 15.3 volts, but avoid recharging a frozen battery. When charging a lead-calcium/calcium maintenance free or AGM battery, add .2 volts to the charging voltage. When charging a deep cycle lead-antimony/antimony or gel cell battery, subtract .4 volt.]

If left unattended, cheap, unregulated trickle or manual battery chargers can overcharge your battery because they can "boil off" the electrolyte. Avoid using fast, high rate, or boost chargers on any battery that is sulfated or deeply discharged. A sulfated battery requires a constant current from one to two amps for 60 to 120 hours. The electrolyte should NEVER bubble violently while recharging because high currents only create heat and excess explosive gasses.


Parasitic (key off) is the cumulative load produced by electrical devices, for example, clocks, computers, alarms, etc., that operate after the engine is stopped. Parasitic loads typically run 20 to 120 milliamps. To test the parasitic load, an ammeter should be inserted in series with the negative battery cable without the engine running. If the parasitic load is prematurely discharging your battery, start removing fuses one-at-a-time until the offending electrical component is identified. Glove box, trunk, and under hood lights that do not automatically turn off are the most common offenders. Leaving your headlights on will generally discharge a fully charged battery (with 90 minutes of Reserve Capacity) within a couple hours.


A. Keeping your battery and engine well maintained is the BEST way to extend the life of your battery.

For cold climates, keeping the battery fully charged and the engine warm will help increase the life of the battery. In the warmer climates and during the summer, the electrolyte levels need to be checked more frequently and DISTILLED water added, if required. This is due to the high underhood temperatures. In a study conducted by the Society of Automotive Engineers, the underhood temperature has increased 30% since 1985. Heat shields are becoming more popular and are being used by a number of car manufacturers to protect the batteries from the high underhood temperatures. Some battery manufacturers build "hot climate" versions by increasing the amount of electrolyte in the battery to provide more "cooling" or by special plate formulations. Batteries last approximately two thirds as long in hot climates as cold ones.

B. Add distilled water--NEVER add acid or tap water and AVOID OVERFILLING.

C. Turning off unnecessary accessories and lights BEFORE starting your car will decrease the load on the battery while cranking, especially when it is cold.

D. Leaving your lights or other accessories on and fully discharging the battery can ruin your car battery, especially if it is maintenance free. If this should this occur, you should test the battery AFTER it has been fully recharged to determine if there is any latent or permanent damage.

E. Reduce the parasitic (key-off) load to 120 milliamps or less.

F. In cold climates, increasing the diameter (smaller wire gauge) of the battery cables will increase the power available to the starter motor.


A. Loss of electrolyte (which account for over 50% of the failures) due to underhood heat or overcharging,

B. Deep discharges (leaving your lights on),

C. Misapplication or using an undersized battery,

D. Undercharging or loose alternator belt,

E. Excessive vibration (due to a loose holdown clamp),

F. Using tap water,

G. Corrosion, and

H. Freezing.


Batteries naturally self discharge while in storage and sulfation will occur over time. Cold will slow the process down and heat will speed it up. Here are five simple steps to store your batteries that will protect them from sulfation and premature failure.

A. Physically inspect for damaged cases, remove any corrosion, and clean the batteries.

B. Check the electrolyte levels and add distilled water as required, but avoid overfilling.

C. Fully charge [equalize] the batteries.

D. Store them in a cool dry place, but not below 10 degrees F.

E. Depending on the ambient temperature, periodically test the state-of-charge using the procedure in Section 4, above. When it is below 80%, recharge [equalize] using the procedures in Section 9, with an automatic [voltage regulated] charger. An alternative would be to connect an automatic [voltage regulated] "trickle" charger to batteries using 13.8 volts and recharge [equalize] the batteries every couple on months. An automatic charge will keep you from overcharging the batteries.


A. Storing batteries 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. [Temperature stratification within large batteries can accelerate the internal "leakage" or self discharge if the battery is sitting on an extremely cold floor in a warm room or installed in a submarine.]

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, running the engine at idle or short "stop-and go trips" during bad weather at night will not recharge the battery.

C. A battery will not explode.

While spark retarding vent caps help, recharging a battery produces hydrogen and oxygen gasses and explosions can occur. They can also occur when the electrolyte level is below the top of the plates. If a spark or flame occurs, an explosion can occur. When this happens, thoroughly wash the engine compartment with a solution of 50% baking soda and water to neutralize the battery acid. Then thoroughly rewash the engine compartment with water. Periodic preventive maintenance and working on batteries in well ventilated areas can reduce the possibility of battery explosions.

D. A battery will not lose it's charge sitting in storage.

A battery has self-discharge or internal electrochemical "leakage" that will cause it to become fully discharged and sulfated over time. Prior to storing a battery, it should be fully charged, placed in a cool location above 10 degrees F, and recharged when it reaches the 80% state-of-charge level or once every two months, whichever occurs first. If left in a vehicle, disconnect the negative cable to reduce the level of discharge.

E. Maintenance free batteries never requires electrolyte.

In hot climates, the electrolyte is "vaporized" or "boiled off" due to the high underhood temperatures. Electrolyte can also be lost due to excessive charging voltage or charging currents. Non-sealed batteries are recommended in hot climates so they can be refilled with distilled water when this occurs.

F. Test the alternator by disconnecting
the battery with the engine running.

A battery acts as a voltage stabilizer or filter to the pulsating DC produced by the alternator. Disconnecting a battery while the engine is running can destroy the sensitive electronic components, for example, emission computer, audio system, cell phone, alarm system, etc., or the charging system because the voltage can rise to 40 volts or more. In the 1970s, removing a battery terminal was an accepted practice to test charging systems of that era. That is not the case today. Just say NO if anyone suggests this.

G. Pulse chargers, aspirins or additives will revive sulfated batteries.

Using pulse chargers or additives is a very controversial subject. Most battery experts agree that there is no proof that more expensive pulse chargers work any better than constant voltage chargers to remove sulfation. They also agree that there is no evidence that additives or aspirins provide any long term benefits.

H. On real cold days turn your headlights on to "warm up" the battery up before starting your engine.

While there is no doubt that turning on your headlights will increase the current flow in a car battery, it also consumes valuable capacity that could be used to start the engine; and therefore, is not recommended. For extremely cold temperatures, externally powered battery warmers or blankets and engine block heaters are highly recommended.


Most of the battery manufacturers have a Battery FAQ posted on their web sites and addition to product information. Web addresses will often change, so you can use an Internet search tool like or to locate the new addresses.

The Battery Related Links are here.

Comments are always welcomed by Bill Darden ( . Copies of the Car and Deep Cycle Battery FAQ's are available from Bill by e-mail.