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Car And Deep Cycle Battery

Frequently Asked Questions

What are the Myths about Car Batteries?

Storing batteries on a concrete floor will discharge themDriving a car will fully recharge a batteryA battery will explodeA battery will lose its charge sitting in storageWet Maintenance Free batteries never require maintenanceTest an alternator by disconnecting the battery with the engine runningConditioners, aspirins or additives will revive sulfated batteriesOn really cold days turn your headlights on to 'warm up' the battery up before starting your engineCar batteries last longer in cold climates than in hot onesCharging cables will start your carA larger capacity battery will damage my carLead-acid batteries have memoriesBad batteries can harm the charging system or starterOnce formed, batteries will not change polarityDo not use tap water to refill batteries

14.1. MYTH: Storing batteries on a concrete floor will discharge them.

False! All lead-acid batteries will naturally self-discharge which can result in loss of capacity from sulfation. The rate of self-discharge is most influenced by the temperature of the battery's electrolyte and the chemistry of the plates. This self-discharge is often mistaken for concrete floor causing the battery to drain. Some experts believe that storing car or deep cycle batteries on a colder concrete floor might actually slow down the self-discharge (leakage) rate because the floor acts as a heat sink and cools the battery. (Please see Section 13 for more information on storing batteries and Section 1 for more information on sulfation.

In the early 1900s, when battery cases were made of porous materials such as tar-lined wood boxes, storing batteries on concrete floor would accelerate their natural self-discharge due to external leakage. Modern battery cases are made of polypropylene or hard rubber. These cases are sealed better, so external leakage-causing discharge is no longer a problem, provided the top of the battery is clean and free from wet or dried electrolyte and the same temperature as the floor.

Large differences in temperature could cause electrolyte stratification within very large batteries (>250 AH) which could accelerate it's internal "leakage" or self-discharge if the battery is sitting on an extremely cold concrete, stone or steel floor in a warm room, boat or submarine. Stirrers or bubblers are often used on these types of large batteries to keep the electrolyte from stratifying. Undercharging will also cause electrolyte stratification, which can also result in loss of capacity from sulfation.

14.2. MYTH: Driving a car will fully recharge a battery.

There are a number of factors affecting a vehicle charging system's ability to recharge a battery, such as how much power and charging voltage from the alternator is diverted to the battery, how long the power is available, and the temperature. Generally, idling the engine or short stop-and-go trips during bad weather or at night will not fully recharge a car battery or will leave your battery undercharged which causes sulfation. When a dead battery needs to be recharged, it is best to use an external battery charger because you could overheat and damage your vehicle's charging system and your will save a lot of gas and wear and tear on your engine. Please see Section 5 and Section 9 for more information on vehicle charging systems and charging.

If jump starting is required to start an engine, the battery should be fully charged by an external charger and then tested for latent damage. Assuming that a car battery has a 50 amp hour capacity and the vehicle's charging system is capable of recharging it at 50 amps at highway speeds, it would take approximately 120 minutes to fully recharge a good battery. If the battery is frozen, install another fully charged battery until the original battery can be thawed out, fully recharged and tested or tow the vehicle to a heated garage. Vehicle charging systems are not designed to recharge fully discharged batteries and doing so may damage the stator windings or the diodes (from overheating).

14.3. MYTH: A battery will explode.

Charging a wet lead-acid battery naturally produces hydrogen and oxygen gasses as electrolysis of the water occurs and needs to occur in well ventilated areas. While spark retarding vent caps help prevent external battery explosions, sparks occur when jumping, connecting or disconnecting charger or battery cables and ignite the gas causing an explosion. From the U.S. Department of Energy, DOE-HDBK-1084-95, "Precautions must be routinely practiced to prevent explosions from ignition of the flammable gas mixture of hydrogen and oxygen formed during overcharge of lead-acid cells. The maximum rate of formation is 0.42 L of hydrogen and 0.21 L of oxygen per ampere-hour overcharge at standard temperature and pressure. The gas mixture is explosive when hydrogen in air exceeds 4% by volume." Less common internal explosions usually occur while starting the engine or using the battery and normally just blow the filler caps or cover off the battery and splatter electrolyte all over the engine compartment or battery box.

The most probable cause of internal battery explosions are from a combination of low electrolyte levels below the plates in the battery, a low resistance bridge is formed between or across the top of the plates, and a build up of hydrogen gas in the cell. The low resistive bridge is called "treeing" between the positive and negative plates. When current flows in the battery, a spark occurs and ignites the residual gas in one or more of the cells. A second possible cause is a manufacturing defect in the weld of one of the plate connecting straps causing a spark igniting the residual gas. Another source of internal battery explosions are caused from direct electrical shorts across the battery's terminals. The battery rapidly over heats form the high current and can explode. The largest number of internal battery explosions occur in hot climates due to the loss of water while starting the engine. Most internal battery explosions could have been prevented if the plates were always covered with electrolyte. Please see Section 3 for more information on preventive maintenance.

A less common form of internal battery explosion occurs when a dead short is applied across the battery terminals or the battery is in a fire.


Periodic preventive maintenance (Please see Section 3.), working on batteries in well-ventilated areas, or using sealed AGM (Ca/Ca) or Gel Cell (Ca/Ca) type batteries can significantly reduce the possibility of battery explosions. To neutralize residual battery acid, be sure to thoroughly wash the engine compartment and the back of the hood with a solution of one-pound baking soda (bicarbonate of soda) to one gallon of warm water and rinse thoroughly with water. While not fatal, each year battery explosions cause thousands of eye and burn injuries from the electrolyte (battery acid). According to PREVENT BLINDNESS AMERICA, in 2003 nearly 6,000 motorists suffered serious eye injuries from working around car batteries. Should a battery explosion occur and battery electrolyte (battery acid) gets in someone's eyes, flush them out with any drinkable liquid immediately because SECONDS count, continue flushing with water for at least 15 minutes, and seek immediate medical attention.

14.4. MYTH: A battery will lose its charge sitting in storage.

Depending on the type of battery and temperature, batteries have a natural self-discharge or internal electrochemical "leakage" at a 1% to 60% rate per month. Over time the battery will become sulfated and fully discharged which make it more susceptible to freezing. Higher temperatures will significantly accelerate this process. A battery stored at 95° F (35° C) will self-discharge twice as fast than one stored at 75° F (23.9° C). Leaving a battery in a vehicle can increase the discharge of battery due to the additional parasitic (ignition key-off load), unless the ground, normally negative, cable is disconnected from the battery. (Please see Section 15 and Section 16 for more information on parking times and sulfation.)

14.5. MYTH: Wet "Maintenance Free" (Ca/Ca) batteries never require maintenance.

The term "Maintenance Free" generally refers to a wet, sealed lead-acid car and deep cycle batteries with calcium positive and negative plates. In hot climates, the water is lost due to evaporation caused by high underhood temperatures and normal charging. Water can also be lost due to excessive charging voltage or charging currents. Using non-sealed wet Low Maintenance (Sb/Ca) batteries (with filler caps) is encouraged in hot climates so distilled, deionized or demineralized water can be added when this occurs. (Please see Section 3. for other preventive maintenance procedures that should be performed on wet "Maintenance Free" (Ca/Ca) batteries.)

14.6. MYTH: Test an alternator by disconnecting the battery with the engine running.

A battery acts like a voltage stabilizer or filter to the pulsating DC produced by the alternator. Disconnecting a battery while the engine is running could destroy the sensitive electronic components connected to the electrical system such as the emission computer, radio, audio system, cell phone, alarm system, etc., or the charging system, especially with internal voltage regulators, because the peak 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. Static electricity and spikes from connecting and disconnecting batteries or test equipment could also damage sensitive electronic components.

14.7. MYTH: Conditioners, aspirins or additives will revive sulfated batteries.

Most battery experts agree that there is no evidence that conditioners, additives or aspirins provide any long-term benefits. Short term gains are achieved by increasing the acidity (Specific Gravity) of the battery, which could increase the Amp Hour capacity, but increase the water consumption and positive grid corrosion and it will also decrease the overall service life of the battery. After a heavy discharge, allowing a battery to rest will regain some of its capacity as the electrolyte has an opportunity to diffuse in the pores of the plates. If the Specific Gravity of a cell requires adjustment, please see Section 9.14.

This controversy between the additive manufacturers, battery manufacturers, and independent electrochemists has been going on for over 50 years as demonstrated in this AD-X2 Battery Additive, From a Trickle to a Torrent article form the National Institute of Standards and Technology (NIST) Museum.

14.8. MYTH: On really 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 cold engine. Therefore, this is not recommended. For cold temperatures, externally powered temperature compensated battery "float" chargers, warmers or blankets, and engine block heaters are highly recommended if the vehicle can not be parked in a heated garage. AGM (Ca/Ca) and Ni-Cad batteries will perform better than wet lead-acid batteries in extremely cold temperatures.

14.9. MYTH: Car batteries last longer in cold climates than in hot ones.

Car batteries last an average of two thirds as long in hot climates as cold ones. Heat kills car batteries, especially sealed Maintenance Free (Ca/Ca) batteries, and cold reduces the battery's starting capacity. (Please see Section 11.1 for more information on increasing battery life.)

14.10. MYTH: Charging cables will start your car.

The cigarette lighter charging cable's advertising states "charges weak batteries in minutes." There is little doubt that charging cable products will certainly increase the charge in your car battery if you have enough time and your battery is in good condition. Cigarette lighters are normally fused at 10 amps, so to be safe they probably limit current to flow less than the fuse size. Given the diameter of the wire used in the cable, the amount might be even less.

They work by applying higher voltage from the vehicle with the good battery to "charge" the bad one. In order to charge a battery the charging voltage needs to be approximately two volts greater than the battery voltage to overcome the internal resistance. Now let's assume it is a hot day and that you need just of 3% of the battery's capacity to start the engine from a 40 amp hour battery. This means you will need at least 7.5 amps for 10 minutes to flow from the good battery with the engine idling to the bad one. Now let's also assume that it is below freezing and you have left your lights on. You will need at least 50% capacity or 20 amp hours to start the vehicle. This will take over two hours to partially charge the dead battery. Using jumper cables with the engine running at high idle will partially charge a dead battery much faster. Please see Section 6 for jump starting, but be sure the battery is not frozen or the case is not cracked.

14.11. MYTH: A larger capacity battery will damage my car.

A starter motor will only use a fixed amount of current from the battery, based on the resistance of the motor. A larger Cold Cranking (CCA), Reserve Capacity (RC) or Amp Hour (AH) capacity battery supplies only what is required. It will not damage your vehicle; however, using batteries with higher or lower voltage or physically too high could potentially cause harm.

14.12. MYTH: Lead-acid batteries have memories.

Lead-acid batteries do not have the "memory effect" mistakenly identified with first generation Ni-Cad batteries; however, continuous undercharging will lower the capacity of the battery over time due to the accumulation of permanent lead-sulfate or "sulfation". Deep discharges below twenty percent State-of-Charge (approximately 12.0 volts) can damage batteries and will shorten their service lives.

14.13. MYTH: Bad batteries can harm the charging system or starter.

A bad or weak starting battery causes additional stress on a charging system, starter motor or starter solenoid. It can cause premature failures due to compensating for the voltage or current. If you replace a battery, alternator, voltage regulator or starter, you should test the other components for damage and repair or replace them as required.

14.14. MYTH: Once formed, batteries will not change polarity.

If a battery is fully discharged and continues to have a load, for example leaving the headlights on, it is possible for one or more cells to reverse polarity. When the battery has been recharged with reversed polarity the polarity can change. This is referred to as "cell reversal". To change polarity, fully discharge the battery and recharge it with the correct polarity.

14.15. MYTH: Do not use tap water to refill batteries.

Use only distilled, deionized or demineralized water to replace the lost water in batteries. This is because using tap or reverse osmosis water from residential systems can produce calcium or magnesium sulfate crystals that can fill the pores and coat the plates. In other words, wet batteries will have a longer service life if you do not use tap water. In an emergency, use rain water because rain water does not contain calcium or magnesium.

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