A word of caution. Batteries contain a sulfuric acid electrolyte which is a highly corrosive poison, that will produce gasses when recharged and explode if ignited. This will hurt you--BAD! When working with batteries, you need to have plenty of ventilation, remove jewelry, wear protective clothing and eye wear (safety glasses), and exercise caution. Whenever possible, please follow the manufacturer's instructions for testing, jumping, installing and charging.
This FAQ assumes a 12 volt, six cell, negative grounded, lead acid battery found in most recreational applications in North America and temperature in degrees Fahrenheit. For six volt batteries, divide the voltage by two; for eight volt batteries, divide by 1.5; for 24 volt batteries, double the voltage; and for 48 volt batteries, multiple by four.
The technical stuff is in [brackets].
1. WHAT IS THE BOTTOM LINE? 1.1. Remove the surface charge before testing and check specific gravity in each cell. (Please see Section 3.) 1.2. Recharge as soon as possible after discharge. (Please see Section 6.) 1.3. Size charger so that it will recharge the battery over an eight to ten hour period. (Please see Section 6.) 1.4. Buy the freshest and largest ampere hour battery that will fit your requirements. (Please see Section 4.) 1.5. Perform preventative maintenance, especially during hot weather. (Please see Section 7.7.) 1.6. The shallower the average discharge, the longer the battery life . (Please see Section 7.5.) 1.7. Temperature matters! 2. WHY BOTHER? Because only the rich can afford cheap batteries..... A good quality deep cycle lead acid battery will cost between $50 and $200 and,if properly maintained, will give you at least 150 deep discharge cycles. The purpose of a deep cycle battery is to provide power for trolling motors, golf carts, fork lift trucks, uninterruptible power supplies (UPS), and other accessories for marine and recreational vehicle (RV) and commercial applications. Dead batteries almost always occur at the most inopportune times, for example, across the lake or during bad weather or on the 17th tee. [A twelve volt deep cycle battery is made up of six cells, each producing 2.1 volts that are connected in series positive to negative. Each cell is made up of an element containing positive plates that are all connected together and negative plates, which are also all connected together. They are individually separated with thin sheets of electrically insulating, porous material that are used as spacers between the positive and negative plates to keep them from shorting to each other. The plates, within a cell, alternate with a positive plate, a negative plate and so on. A plate is made up of a metal grid that serves as the supporting framework for the active material which is "pasted" on it. The cells are inserted into a polypropylene case, connected to the terminals, covered, filled with a dilute sulfuric acid electrolyte and formed (initially charged). The electrolyte is replaced and the battery is given a finishing charge. A battery is created when two different metals such as Lead Dioxide (Pb O2), the positive plates, and Sponger lead (Pb), the negative plates, are immersed in Sulfuric Acid (H2SO4), the electrolyte. The types of metals and the electrolyte used will determine. A typical lead-acid battery produces approximately 2.1 volts per cell. The chemical action between the metals and the electrolyte creates the electrical energy, that flows from the battery as soon as there is a load, such a light bulb, between the positive and negative terminals. The electrical current flows as charged portions of acid (ions) between the battery plates and as electrons through the external circuit. The action of the lead-acid storage battery is determined by chemicals used, temperature, and load.] Normally a battery "ages" as the active positive plate material sheds (or flakes off) due to the expansion and contraction that occurs during the discharge and recharge cycles, the positive grid metal corrodes in the electrolyte, or the negative grid shrinks. Deep discharges, heat, vibration, over charging, or non-use accelerate this "aging" process. Sediment or "mud" builds up in the bottom of the case and the can short the cell out. Another major cause of premature battery failure is sulfation. When batteries are stored discharged or stored fully charged for over three months without being recharged, the plates slow discharge and become coated with hard and dense layer of lead sulfate. Over time, the battery can not be recharged. Using tap water to refill batteries can produce calcium sulfate, which also will coat the plates. Recharging a sulfated battery is like trying to wash your hands with gloves on. When the active material in the plates can no longer sustain a discharge current and the battery "dies". Most of the "defective" batteries that are returned to the manufacturer during free placement warranty periods are good. This suggests that most sellers of new batteries do not know how or take the time to properly load test or recharge batteries. 3. HOW DO I TEST A BATTERY? There are six simple steps in testing a deep cycle battery--inspect, recharge, remove surface charge, measure the state-of-charge, load test, and recharge. If you have a non-sealed battery, it is highly RECOMMENDED that you use a temperature compensated hydrometer, which can be purchased, at an auto parts store between $5 and $20. A hydrometer is a float type device used to determine the state-of-charge by measuring the specific gravity of the electrolyte in each cell. It is a very accurate way of determining a battery's state-of-charge and weak or dead cells. To troubleshoot charging or electrical systems or if you have a sealed battery, 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, between $20 and $200. Analog voltmeters are not accurate enough to measure the millivolt differences of the battery's state-of-charge or the output of the charging system. A battery load tester is optional. 3.1. INSPECT Visually inspect for obvious problems, for example, loose of broken alternator belt,electrolyte levels BELOW the top of the plates, corroded or swollen cables,corroded terminal clamps loose hold-down clamps, loose cable terminals, or leaking or damaged battery case. If the electrolyte levels are low in non-sealed batteries, allow the battery to cool and add DISTILLED water to the level indicated by the battery manufacturer or to 1/4 inch BELOW the bottom of the plastic filler tube (vent wells). The plates need to be covered at all times and avoid OVERFILLING, especially in hot climates, because the heat will cause the electrolyte to expand and overflow. 3.2. RECHARGE Recharge the battery to 100% state-of-charge. If the battery has a difference of .03 specific gravity reading between the lowest and highest cell, then you should equalize it. (Please see Section 6.) 3.3. REMOVE SURFACE CHARGE Surface charge is the uneven mixture of sulfuric acid and water within the surface of the plates as a result of charging or discharging. It will make a weak battery appear good or a good battery appear bad. You need eliminate the surface charge by one of the following methods: 3.3.1. Allow the battery to sit for four to twelve hours to allow for the surface charge to dissipate. [RECOMMENDED]. 3.3.2. Apply a load that is 33% of the ampere hour capacity for five minutes and wait five to ten minutes. 3.3.3. With a battery load tester, apply a load at one half the battery's CCA rating for 15 seconds and wait five to ten minutes. 3.4. MEASURE THE STATE-OF-CHARGE If the battery's electrolyte is above 100 degrees, allow it to cool. To determine the battery's state-of-charge with the battery's electrolyte temperature at 80 degrees, use the following table, which assumes that 1.265 specific gravity reading is as fully charged battery: Voltmeter Hydrometer Open Circuit Approximate Average Cell Voltage State-of-charge Specific Gravity 12.65 100% 1.265 12.45 75% 1.225 12.24 50% 1.190 12.06 25% 1.155 11.89 Discharged 1.120 [Source: Battery Council International] [Electrolyte temperature compensation, depending on the battery manufacturer's recommendations, will vary. If you are using a NON-temperature compensated HYDROMETER, make the following adjustments, and if the temperature of the electrolyte is BELOW 80 degrees, SUBTRACT .004 specific gravity per 10 degrees below 80 degrees FROM the Specific Gravity indicated in the table above. For example, at 30 degrees, the specific gravity reading would be 1.245 for a 100% state-of-charge. If the temperature of the electrolyte is ABOVE 80 degrees, then ADD .004 specific gravity per 10 degrees above 80 degrees TO the Specific Gravity. For example, at 100 degrees, the specific gravity would be 1.273 for 100% state-of-charge. This is why using a temperature compensated hydrometer is highly RECOMMENDED and more accurate. If you are using a digital VOLTMETER, then from the table above make the following adjustments, if the temperature of the electrolyte is BELOW 80 degrees, SUBTRACT .0012 to .028 volts (1.2 to 28 millivolts) per 10 degrees below 80 degrees from the Open Circuit Voltage indicated. For example, at 30 degrees and using 28 millivolts, the reading would be 12.51 VDC at 100% state-of-charge. If the temperature of the electrolyte is ABOVE 80 degrees, then ADD .0012 to .028 volts (1.2 to 28 millivolts) per 10 degrees above 80 degrees. For example, at 100 degrees and using 28 millivolts, the Open Circuit Voltage would be 12.71 VDC.] For non-sealed batteries, check the specific gravity in each cell with a hydrometer and average the readings. For sealed batteries, measure the Open Circuit 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 and recharged before proceeding. If sealed, the battery is toast. 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. You should replace the battery, if one or more of the following conditions occur: 3.4.1. If there is a .05 or more difference in the specific gravity reading between the highest and lowest cell, you have a weak or dead cell(s). If you are really lucky, applying an EQUALIZING charge may correct this condition. (Please see Section 6.) 3.4.2. If the battery will not recharge to a 75% or more state-of-charge level or if the built-in hydrometer still does not indicate "good" (usually green, which is 65% state-of-charge or better). [If you know that a battery has spilled or "bubbled over" and the electrolyte has been replaced with water, you can replace the old electrolyte with new electrolyte and go back to Step 3.2 above. Battery electrolyte is a mixture of 25% sulfuric acid and distilled water. It is cheaper to replace the electrolyte than to buy a new battery.] 3.4.3 If digital voltmeter indicates 0 volts, you have an open cell. 3.4.4. If the digital voltmeter indicates 10.45 to 10.65 volts, you probably have a shorted cell or a severely discharged battery. [A shorted cell is caused by plates touching, sediment "mud" build-up or "treeing" between the plates.] 3.5. LOAD TEST If the battery is fully charged or has a "good" built-in hydrometer indication, then you can test the capacity of the battery by applying known load and measure the time it take to discharge the battery until 20% capacity is remaining. Normally a discharge rate that will discharge a battery in 20 hours can be used [C/20]. For example, if you have a 80 ampere hour rated battery, then a load of four amps would discharge the battery in approximately 20 hours (or 16 hours down to the 20% level). New batteries can take up to 50 charge/discharge cycles before they reach their rated capacity. Depending on your application, batteries with 80% or less of their original capacity are considered history. 3.6. RECHARGE If the battery passes the load test, you should recharge it as soon as possible to restore it to peak performance and to prevent lead sulfation. 4. WHAT DO I LOOK FOR IN BUYING A NEW BATTERY? 4.1. Ampere Hour (or Reserve Capacity) Rating The most important consideration in buying a deep cycle battery is the Ampere Hour (AH) or Reserve Capacity rating that will meet or exceed your requirements and how much weight you can carry. [Most deep cycle batteries are rated in discharge rates of 100 amps, 20 amps, or 8 amps. Higher the discharge, the lower the capacity due to the Peukert Effect and the internal resistance of the battery. Reserve Capacity (RC) is the number of minutes a fully charged battery at 80 degrees is discharged at 25 amps before the voltage falls below 10.5 volts.] To convert Reserve Capacity to Ampere Hours, multiple RC by .6. For example, a battery with 120 minute RC will have approximately 72 Ampere Hours. This means that the battery should produce one amp for 72 hours of continuous use. More ampere hours (or RC) are better in every case. Within a BCI group size, the battery with larger ampere hours (or RC) will tend to weigh more because it contains more lead. [If more ampere hours are required, two new and identical six volt batteries can be connected in series (positive terminal of Battery One to the negative terminal of Battery Two). Two (or more) new and identical 12 volt batteries can be connected in parallel (positive terminals to positive terminals and negative terminals to negative terminals with identical cables). When connecting in series or parallel and to prevent recharging problems, do NOT mix old and new batteries or ones with different types. Cable lengths should be kept short and cable sized large enough to prevent significant voltage drop [.2 volts (200 millivolts) or less] between batteries.] 4.2. Type Car batteries are especially designed for high initial cranking amps (usually 200 to 400 amps for five to 15 seconds) to start a car and not for deep cycle discharges. Deep cycle (and marine) batteries are designed for prolonged discharges at lower current. [The plates in car battery are more porous and thinner than in deep cycle batteries and use sponges or expanded metal grid instead of solid lead.] A deep cycle battery will typically outlast two to ten car batteries when used in deep cycle applications. Starting an engine will typically consume less that 5% of a car battery's capacity. Whereas, deep cycle (or marine) batteries are used for applications that will consume between 20 and 80% of the battery's capacity. A "dual" or starting marine battery is a compromise between a car and deep cycle battery. A deep cycle or "dual marine" battery will work as starting battery if it can produce enough current to start the engine, but not as well as a car battery. For RVs, 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. When the RV's charging system is running, both batteries are automatically recharged. An excellent and easy to understand free booklet on multi-battery applications, "Introduction to Batteries and Charging Systems", can be downloaded from this link or by calling (800) 845-6269 or (503) 692-5360. The two most common types of deep cycle batteries are flooded (also known as wet or liquid electrolyte) cell and valve regulated (VR). 4.2.1. Flooded cell Flooded cell deep cycle batteries are divided, like their car battery counterparts, into low maintenance (the most common) and maintenance free, based on their plate formulation. [Low maintenance batteries have lead-antimony/antimony or lead-antimony/calcium (dual alloy or hybrid) plates; whereas, the maintenance free batteries use lead-calcium/calcium.] The advantages of maintenance free batteries are less preventative maintenance, up to 250% less water loss,faster recharging, greater overcharge resistance, reduced terminal corrosion, up to 40% more life cycles, and up to 200% less self discharge. However, they are more prone to deep discharge (dead battery) failures [due to increased shedding of active plate material and development of a barrier layer between the active plate material and the grid metal], and if sealed, a shorter life in hot climates because lost water can not be replaced. Maintenance free batteries are generally more expensive than low maintenance batteries. 4.2.2. Valve Regulated Valve Regulated Lead Acid (VRLA) batteries are generally divided into two groups, gel cell and Absorbed Glass Mat (AGM). VRLA batteries are spill proof, so they can be used in semi-enclosed areas, are totally maintenance free, and longer shelf life. Their greatest disadvantage is the high initial cost (two to three times), but arguably could have an overall lower cost due to a longer lifetime and no "watering" labor costs, if properly maintained and recharged. 4.3. Size An internationally adopted Battery Council International (BCI) group number (U1, 24, 27, 31, etc.) is based on the physical case size, terminal placement and terminal polarity. Within a group, the ampere hour or RC ratings, warranty and battery type will vary in models of the same brand or from brand to brand. You can also find BCI size information online at Exide. Generally, batteries are sold by model, so some of 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 ampere hour or 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 anything else. 4.4. Freshness Determining the "freshness" of a battery is sometimes difficult. NEVER buy a wet lead acid battery that is MORE than THREE months old because it has starting to sulfate, unless it has periodically been recharged. [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.] Dealers will often place their older batteries in storage racks so they will sell first. The new batteries can often be found in the rear of the rack or in a storage room. 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. If you can not determine the date code then ask the dealer or contact the manufacturer. Like bread, fresher is definitely better and does matter. 4.5. 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 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. 5. HOW DO I INSTALL A BATTERY? 5.1. Thoroughly wash and clean the old battery, battery terminals and case or tray with warm water to minimize problems from acid or corrosion. Heavy corrosion can be neutralized with a mixture of one pound of baking soda to one gallon of warm water. Wear safety goggles and, using a stiff brush, brush away from yourself. Also, mark the cables so you do not forget which one to reconnect. 5.2. 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 sulfuric acid. 5.3. After removing the old battery, be sure that the battery tray or box and cable terminals or connectors are clean. Auto parts stores sell a cheap wire brush that will allow you to clean the inside of terminal clamps and the terminals. If the terminals, cables or hold down brackets are severely corroded, replace them. Corroded terminals or swollen cables will significantly reduce starting capability. 5.4. Use red and green paraffin oil-soaked felt washer pads [RECOMMENDED] found at auto parts stores or thinly coat the terminal, terminal clamps and exposed metal around the battery with a high temperature grease or petroleum jelly (Vaseline) to prevent corrosion. Do not use the felt washers between the mating conductive surfaces with side terminal batteries. 5.5. 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. 5.6. After replacing the hold-down bracket, reconnect the cables in reverse order, i.e., attach the POSITIVE cable first and then the NEGATIVE cable last. 5.7. Before using the battery, check the electrolyte levels and add distilled water to cover the plates. Check the state-of-charge and recharge if necessary. Then recheck the electrolyte levels after the battery has cooled and top off with distilled water as required, but do not overfill. 6. HOW DO I RECHARGE (OR EQUALIZE) MY BATTERY? There are three phases of battery charging--bulk, absorption and float. The bulk stage is where you can give the battery whatever current it will accept not to exceed 20% of the ampere hour rating and that will not cause overheating. The absorption phase is voltage-regulated current charging until the battery is fully charged. This is normally when the charging current drops off to 1% or less of the ampere hour capacity of the battery. For example, end current for a 72 ampere hour battery is .7 amps or less. Float charging at a lower voltage is used to maintain a fully charged battery. Please refer to Section 9 for more information about storing batteries and float charging them. Equalizing is a controlled 5% overcharge to equalize and balance the voltage and specific gravity in each cell of a wet lead acid battery. Equalizing reverses the build-up of the chemical effects like stratification where acid concentration is greater in the bottom of the battery. It also helps remove sulfate crystals that might have built up on the plates. The frequency recommendation varies by manufacturer from once a month to once a year, 50 to 100 deep cycles, or a specific gravity difference between cells of .03 or .015 volts (15 millivolts). To equalize, fully recharge the battery. Then increase the charging voltage to the manufacturer's recommendations, or if not available, ADD 5%. Heavy gassing should start occurring. Take specific gravity readings in each cell once per hour. Equalization has occurred once the specific gravity values no longer rise during the gassing stage. It is important to use the battery manufacturer's charging recommendations whenever possible for optimum performance and life. In addition to the earlier cautions, here are some more words of caution: 6.1. NEVER, NEVER disconnect a battery cable from vehicle with the engine running because the battery acts like a filter for the electrical system. Unfiltered [pulsating DC] electricity can damage expensive electronic components, e.g., emissions computer, radio, charging system, etc. 6.2. For non-sealed batteries, check the electrolyte level and be sure it is covering the plates and is not frozen BEFORE recharging. 6.3. Do NOT add distilled water if the electrolyte is covering the top of the plates because during the recharging process, it will warm and expand. After recharging has been completed, RECHECK the level. 6.4. Reinstall the vent caps BEFORE recharging and recharge ONLY in well ventilated areas. NO smoking, sparks or open flames while the battery is being recharged because batteries give off explosive gasses. 6.5. If your battery is an AGM or a sealed flooded type, do NOT recharge with current ABOVE 12% of the battery's RC rating (or the 20% of the ampere hour rating). Gel cells should be charged over a 20 hour period and never over the manufacturer's recommended level or 14.1 VDC. 6.6. Follow the charger manufacturer's procedures for connecting and disconnecting cables and operation to minimize the possibility of an explosion, but generally you should turn the charger OFF before connecting or disconnecting cables to a battery. Good ventilation or a fan is recommended to disperse the gasses created by the recharging process. 6.7. If a battery becomes hot (over 125 degrees) or violent gassing or spewing of electrolyte occurs, turn the charger off temporarily or reduce the charging rate. 6.8. Insure that charging with the battery in the car with an external MANUAL charger will not damage the vehicle's electrical system with high voltages. If this is even a remote possibility, then disconnect the vehicle's negative battery cable from the battery BEFORE connecting the charger. 6.9. If you are recharging gel cell batteries, manufacturer's charging voltages can be very critical and you might need special recharging equipment. In most cases, deep cycle chargers used to recharge wet batteries can not be used to recharge gel cell and AGM batteries because of their higher charging voltage. 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 discharged batteries, the following table lists the recommended battery charging rates and times: Reserve Capacity Slow Charge Fast Charge (RC) Rating 80 Minutes or less 15 Hours @ 3 amps 5 Hours @ 10 amps 80 to 125 Minutes 21 Hours @ 4 amps 7.5 Hours @ 10 amps 125 to 170 Minutes 22 Hours @ 5 amps 10 Hours @ 10 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 [Source: Battery Council International] The BEST method is to SLOWLY recharge the battery at 70 degrees over eight hour period using an external constant voltage (or tapered current charger) because the acid has more time to penetrate the plates. [RECOMMENDED] A constant voltage "automatic" charger applies regulated voltage at approximately 13.8 to 16 volts based on the manufacturer's recommendations and temperature. A 10 amp automatic charger will cost between $30 and $60 at an auto parts store. Some sulfated batteries, depending on the size and degree of sulfation, can be recovered by applying one or two amps for 48 to 120 hours. [An excellent automatic constant voltage battery charger is a 15 volt regulated power supply adjusted to the manufacturer's recommendations or, if not available, to voltages below with the electrolyte at 70 degrees: Battery Type Charging Float Equalizing Wet Low Maintenance 14.4 13.2 15.1 Wet Maintenance Free 14.8 13.6 15.5 AGM 14.6 13.8 N/A Gel Cell 14.0 13.5 N/A Wet Deep Cycle 15.0 13.2 15.8 To compensate for electrolyte temperature, adjust the charging voltage .0028 (2.8 millivolts) to .0033 (3.3 millivolts) volts/cell/degree. For example, if 30 degrees, then INCREASE the charging voltage to 15.19 volts for a wet low maintenance battery. If 100 degree, then DECREASE the charging voltage to 13.81 volts.] If left unattended, a cheap, unregulated trickle battery charger 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. The electrolyte should NEVER bubble violently while recharging because high currents only create heat and excess explosive gasses. 7. CAN I INCREASE THE LIFE OF MY BATTERY? 7.1. Recharging slowly and keeping your battery well maintained are the best ways to extend the life of your battery. 7.2. Recharging every two months will prevent lead sulfation. 7.3. In the warmer climates and during the summer "watering" is required more often. Check the electrolyte levels and add distilled water, if required. Never add electrolyte to battery that is not fully charged--just distilled water and do not overfill. The plates must be covered at all times. 7.4. High ambient temperatures (above 80 degrees) will shorten battery life because it increases positive grid corrosion. 7.5. Shallower the average depth-of-discharge (DoD), increases the battery life. For example, a battery with an average of 50% DoD will last twice as long or more as 80% DoD and 20% DoD will five times longer than 50% DoD. For example, golf cart batteries will average 225 cycles at 80% DoD and increase to 750 cycles at 50% DoD. Try to avoid DoD that is less than 10% and greater than 80%. 7.6. Recharge a deep cycle battery as soon as possible after each use. Maintaining the correct state-of-charge while in storage, electrolyte levels, tightening loose hold-down clamps and terminals, and removing corrosion is normally the only preventative maintenance required for a deep cycle battery. 8. WHAT ARE THE MOST COMMON CAUSES OF PREMATURE BATTERY FAILURES? 8.1. Loss of electrolyte due to heat or overcharging, 8.2. Lead sulfation in storage, 8.3. Undercharging with voltages less than 13.8 volts, 8.4. Old age (positive plate shedding), 8.5. Excessive vibration, 8.6. Freezing or high temperatures, 8.7. Using tap water causing calcium sulfation, 8.8. Corrosion. 9. HOW CAN I STORE BATTERIES? Batteries naturally self-discharge 1% to 15% per month while in storage and lead sulfation will occur over time. If left in a vehicle, disconnect the negative cable to reduce the level of discharge. Cold will slow the process down and heat will speed it up. Use the following six simple steps to store your batteries: 9.1. Physically inspect for damaged cases, remove any corrosion, and clean the batteries. 9.2. Fully recharge the batteries. 9.2. Check the electrolyte levels and add distilled water as required, but avoid overfilling. 9.4. Store them in a cool dry place, but not below 32 degrees. 9.5. Depending on the ambient temperature and self-discharge rate, periodically test the state-of-charge using the procedure in Section 4. When it is below 80%, recharge the batteries using the procedures in Section 6. An alternative would be to connect an automatic [voltage regulated], solar panel or "smart trickle" charger to "float" batteries using, based on the manufacturer's recommendations or 13.02 to 13.8 volts for wet batteries and 13.38 to 14.1 volts for VRLA batteries, compensated for temperature. An automatic or smart charger will prevent you from overcharging the batteries. 9.6 Equalize only wet or flooded batteries when you remove the batteries from storage using the procedure in Section 6. 10. WHAT ARE SOME OF THE MYTHS ABOUT BATTERIES? 10.1. 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. [Temperature stratification within very large batteries could 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.] 10.2. Driving a car will fully recharge a battery. There are a number of factors affecting charging system'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 or hot weather at night will not recharge a battery. 10.3. 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 rinse the engine compartment with water, then wash with a solution of one pound baking soda to one gallon of water to neutralize the residual 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. 10.4. A battery will not lose its charge sitting in storage. A battery has self-discharge or internal electrochemical "leakage" at a 1% to 15% rate per month that will cause it to become sulfated and fully discharged over time. (Please see Section 9.) 10.5. Wet maintenance free batteries never require water. In hot climates, the water is "vaporized" or "boiled off" due to the high underhood temperatures. Water 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. 10.6. Test the alternator by disconnecting the battery with the engine running. A battery as like a voltage stabilizer or filter to the pulsating DC produced by the charging system. 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. 10.7. 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 conclusive proof that more expensive pulse charges 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. 10.8. 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, battery blankets, engine block heaters or AGM batteries are highly RECOMMENDED. 11. HOW LONG WILL A DEEP CYCLE BATTERY LAST ON A SINGLE CHARGE? Discharging, like charging, depends on a number of factors. The important ones are the initial state-of-charge, depth-of-discharge, age, capacity of the battery, load and temperature. For a fully charged battery at 70 degrees, the ampere hour rating divided by the load in amps will provide the estimated life of that cycle. For example, a 72 ampere hour battery with a 10 amp load should last approximately 7.2 hours. 12. WHERE CAN I FIND MORE INFO ON BATTERIES? Additional information sources about deep cycle batteries can be found in the Battery Related Links on the Web server at Battery Links 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 www.google.com or www.dogpile.com to locate the new addresses. Comments are always welcomed by Bill Darden at mailto:firstname.lastname@example.orgFor additional information on car batteries, the Car Battery FAQ maybe found on the Web server at The Car Battery FAQ or by requesting one via email from mailto:email@example.com:.