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Battery FAQ

Questions & Answers

Batteries are devices that convert stored chemical energy into useful electrical energy. A battery consists of two or more galvanic cells connected in series or parallel. A galvanic cell consists of a negative electrode; an electrolyte, which conducts ions; a separator, an ion conductor; and a positive electrode..
The internal workings of a battery are typically housed within a case. Inside this case are a cathode, which connects to the positive terminal, and an anode, which connects to the negative terminal. These components, more generally known as electrodes, occupy most of the space in a battery and are the place where the chemical reactions occur. A separator creates a barrier between the cathode and anode, preventing the electrodes from touching while allowing electrical charge to flow freely between them. The medium that allows the electric charge to flow between the cathode and anode is known as the electrolyte. Finally, the collector conducts the charge to the outside of the battery and through the load.
There are three main components of a battery: two terminals (one terminal is marked (+), or positive, while the other is marked (-), or negative) made of different chemicals (typically metals), the anode and the cathode..; and the electrolyte, which separates these terminals. The electrolyte is a chemical medium that allows the flow of electrical charge between the cathode and anode. When a device is connected to a battery—a light bulb or an electric circuit—chemical reactions occur on the electrodes that create a flow of electrical energy to the device.
The anode (current-sink) of a battery is the terminal where current flows in from outside. When the battery is discharging the anode is the negative terminal since that is where the current flows into the battery cell. When dealing with batteries, it is best not to think in terms of anode and cathode; think in terms of positive terminal and negative terminal.
The cathode (current-source) of a battery is the terminal where current flows out. When the battery is charging the anode is the positive terminal, which receives current from an external source (i.e. battery charger). When dealing with batteries, it is best not to think in terms of anode and cathode; think in terms of positive terminal and negative terminal.
An electrolyte is a liquid of gel that acts as a mediumto conduct electricity. Electrolytes allow ions to travel between the cathode and the anode to keep the electrical process underway, while keeping the reactive oxigen and hydrogen apart,
A battery "cycle" is one complete discharge and recharge cycle. It is usually considered to be discharging from 100% to 20%, and then back to 100%. However, there are often ratings for other depth of discharge cycles; the most common ones are 10%, 20%, and 50%.
Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% Depth of Discharge (DOD). If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. The most practical number to use is 50% DOD on a regular basis.
In many types of batteries, the full energy stored in the battery cannot be withdrawn (in other words, the battery cannot be fully discharged) without causing serious, and often irreparable damage to the battery. The Depth of Discharge (DOD) of a battery determines the fraction of power that can be withdrawn from the battery. For example, if the DOD of a battery is given by the manufacturer as 25%, then only 25% of the battery capacity can be used by the load. Nearly all batteries, particularly for renewable energy applications, are rated in terms of their capacity. However, the actual energy that can be extracted from the battery is often (particularly for lead acid batteries) significantly less than the rated capacity. This occurs since, particularly for lead acid batteries, extracting the full battery capacity from the battery dramatically reduced battery lifetime. The depth of discharge (DOD) is the fraction of battery capacity that can be used from the battery and will be specified by the manufacturer. For example, a battery 500 Ah with a DOD of 20% can only provide 500Ah x .2 = 100 Ah.
In addition to specifying the overall depth of discharge, a battery manufacturer will also typically specify a daily depth of discharge. The daily depth of discharge determined the maximum amount of energy that can be extracted from the battery in a 24 hour period. Typically in a larger scale PV system (such as that for a remote house), the battery bank is inherently sized such that the daily depth of discharge is not an additional constraint. However, in smaller systems that have relatively few days storage, the daily depth of discharge may need to be calculated.
A key parameter of a battery in use in a Photovoltaic system is the battery state of charge (SOC). The BSOC or SOC is defined as the fraction of the total energy or battery capacity that has been used over the total available from the battery. Battery state of charge (SOC) gives the ratio of the amount of energy presently stored in the battery to the nominal rated capacity. For example, for a battery at 80% SOC and with a 500 Ah capacity, the energy stored in the battery is 400 Ah. A common way to measure the SOC is to measure the voltage of the battery and compare this to the voltage of a fully charged battery. However, as the battery voltage depends on temperature as well the state of charge of the battery, this measurement provides only a rough idea of battery state of charge.
Batteries must be handled with care. They contain sulfuric acid (the electrolyte) and fragile lead-antimony or lead-calcium plates. The case, made of plastic or hard rubber, can be damaged by rough handling. Cable clamps should fit properly without the need to hammer them onto the posts, possibly damaging the battery. Flush mounted cable connections should be tightened with care; tightening too much may result in damage to the battery. Use care in removing cables; too much force can result in battery damage.
Yes…..The electrolyte in a battery is sulfuric acid. It is strong when the battery is charged and weak when the battery is discharged. The acid can cause severe tissue damage since it is approximately 36 percent sulfuric acid and 64 percent water. It will eat holes in clothing, burn skin, and cause blindness. Even in the discharged state, at 12 percent acid, it can cause burns. Tipping the battery should be avoided since it may cause the acid to spill, with possible injury or damage. Acid must be respected. Lead-acid storage batteries produce hydrogen and oxygen gases when they are charging and discharging. Hydrogen mixed with oxygen is very explosive and can be ignited by a spark or a flame. This may explode the battery case. Always use an electric light to check the electrolyte level, never a match; it could ignite any gases present.
Remove and attach battery cables in the right order. The ground cable should be disconnected first and connected last. If a wrench were to slip while you are working on an ungrounded connection it could complete a circuit with part of the vehicle, produce a spark and ignite any hydrogen gas around the battery. Do not work on a battery while the engine is running. Current may be flowing in or out of the battery, increasing the chance of a spark.
A battery is an electrical storage device. Batteries do not make electricity; they store it, just as a water tank stores water for future use. As chemicals in the battery change, electrical energy is stored or released. In rechargeable batteries this process can be repeated many times.
The Internal resistance (IR) of a battery is the opposition to flow of current within the battery. The internal resistance is converted to heat, which is why batteries get warm when being charged up. The lower the internal resistance, the better. Much of loss of efficiency is due to higher internal resistance at higher amperage rates - internal resistance is not a constant - kind of like "the more you push, the more it pushes back".
Typical efficiency in a lead-acid battery is 85-95%, in alkaline and NiCad battery it is about 65%. True deep cycle AGM's can approach 98% under optimum conditions, but those conditions are seldom found so you should figure as a general rule about a 10% to 20% total power loss when sizing batteries and battery banks.
Practically all batteries used in Photovoltaic (PV) and all but the smallest backup systems are Lead-Acid type batteries which offer the best price to power ratio. A few systems use NiCad, in extremely cold temperatures (-50 F or less). They are expensive to buy, and very expensive to dispose of due the hazardous nature of Cadmium. All of the batteries commonly used in deep cycle applications are Lead-Acid. This includes the standard flooded (wet) batteries, gelled, and AGM. They all use the same chemistry, although the actual construction of the plates and other components varies. NiCads, Nickel-Iron, and other types are found in a few systems, but are not common due to their expense, environmental hazards, and/or poor efficiency.
The major applications are automotive, marine, and deep-cycle. Deep-cycle includes solar electric (PV), backup power, traction, and RV and “boat house" batteries.
The major types, based on its construction, are flooded (wet), gelled, and AGM (Absorbed Glass Mat).
Flooded or Wet Cells are the most common lead-acid battery-type in use today. They have removable caps, or or be sealed ("maintenance free”). In marine applications, they are usually not sealed so the electrolyte can be replenished through 1/2" holes in the top casing of the battery. The battery casing will include molded cells and a grid of lead plates filled with sulphuric acid as an electrolyte. Since the container is not sealed, and the grid only supported on the edges, great care has to be taken to ensure that the electrolyte does not come into contact with the user (burns!) or seawater (chlorine gas!). The water needs of flooded cells can be reduced via the use of Hydrocaps, which facilitate the recombination of Oxygen and Hydrogen during the charging process.
Gel Cell batteries use a thickening agent like fumed silica to immobilize the electrolyte. Thus, if the battery container cracks or is breached, the cell will continue to function. The thickening agent prevents the movement of the electrolyte and cannot be re-filled with electrolyte. Controlling the rate of charge is very important or the battery will be ruined quickly. Gel cells use slightly lower charging voltages than flooded cells and thus the set-points for charging equipment have to be adjusted.
Absorbed Glass Mat (AGM) batteries are the latest step in the evolution of lead-acid batteries. Instead of using a gel, an AGM uses a fiberglass like separator to hold the electrolyte in place. The physical bond between the separator fibers, the lead plates, and the container make AGMs spill-proof and the most vibration and impact resistant lead-acid batteries available today. The AGMs use almost the same voltage set-points as flooded cells and thus can be used as drop-in replacements for flooded cells. Basically, an AGM can do anything a Gel-cell can, only better. However, since they are also sealed, charging has to be controlled carefully or they can be ruined in short order.
All AGM & gelled are sealed and are "valve regulated", which means that a tiny valve keeps a slight positive pressure. Nearly all sealed batteries are "valve regulated" (commonly referred to as "VRLA" - Valve Regulated Lead-Acid). Most valves regulated are under some pressure - 1 to 4 psi at sea level. What is the battery manufacturers recommended ratio between the battery bank size and the electrical load? Deep-Cycle Flooded cell battery manufacturers recommend a 4 to 1 ratio; AGM and Gel cell manufacturers recommend a ratio of at least 3 to 1, between battery bank size and the largest load encountered on board
The lifespan of a deep cycle battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors. Gelled cells can be destroyed in one day when overcharged with a large automotive charger. Golf cart batteries can be destroyed without ever being used in less than a year if left sitting in a hot garage or warehouse without being charged. Even the “dry charged" batteries (where you add acid when you need them) have a shelf life of 18 months at most. (They are not totally dry - they are actually filled with acid, the plates formed and charged, then the acid is dumped out).
There are many variables, such as depth of discharge, maintenance, temperature, how often and how deep cycled, etc. that it is almost impossible to give a fixed number…….Starting: 3-12 months; Marine: 1-6 years; Golf cart: 2-7 years; AGM deep cycle: 4-8 years; Gelled deep cycle: 2-5 years; Deep cycle (L-16 type etc): 4-8 years; Rolls-Surrette premium deep cycle: 7-15 years; Industrial deep cycle (Crown and Rolls 4KS series): 10-20+ years.; Telephone (float): 2-20 years. These are usually special purpose "float service", but often appear on the surplus market as "deep cycle". They can vary considerably, depending on age, usage, care, and type. NiFe (alkaline): 5-35 years and NiCad: 1-20 years.
Starting (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).
Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less "instant" power like starting batteries need. Although these can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge.
Marine batteries are usually a "hybrid", and fall between the starting and deep-cycle batteries, though a few are true deep cycle. In the hybrid, the plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries. It is often hard to tell what you are getting in a "marine" battery, but most are a hybrid. Starting batteries are usually rated at "CCA", or cold cranking amps, or "MCA", Marine cranking amps - the same as "CA". Any battery with the capacity shown in CA or MCA may or may not be a true deep-cycle battery. It is sometimes hard to tell, as the term deep cycle is often overused. CA and MCA ratings are at 32 degrees F, while CCA is at zero degree F. Unfortunately, the only positive way to tell with some batteries is to buy one and cut it open - not much of an option.
It will not hurt a deep cycle battery to be used as a starting battery, but for the same size battery they cannot supply as much cranking amps as a regular starting battery and is usually much more expensive. As a general rule, if you are going to use a true deep cycle battery also as a starting battery, it should be over-sized about 20% compared to the existing or recommended starting battery group size to get the same cranking amps. That is about the same as replacing a group 24 with a group 31. With modern engines with fuel injection and electronic ignition, it generally takes much less battery power to crank and start them, so raw cranking amps is less important than it used to be. On the other hand, many cars, boats, and RV's are more heavily loaded with power sucking "appliances", such as megawatt stereo systems etc. that are more suited for deep cycle batteries.
Sometimes called "fork lift", "traction" or "stationary" batteries, are used where power is needed over a longer period of time, and are designed to be "deep cycled", or discharged down as low as 20% of full charge (80% DOD, or Depth of Discharge). These are often called traction batteries because of their widespread use in forklifts, golf carts, and floor sweepers (from which we get the "GC" and "FS" series of battery sizes). Deep cycle batteries have much thicker plates than automotive batteries. They are sometimes used in larger PV systems because you can get a lot of storage in a single (very large and heavy) battery.
Plate thickness (of the Positive plate) matters because of a factor called "positive grid corrosion". This ranks among the top 3 reasons for battery failure. The positive (+) plate is what gets eaten away gradually over time, so eventually there is nothing left - it all falls to the bottom as sediment. Thicker plates are directly related to longer life, so other things being equal, the battery with the thickest plates will last the longest. The negative plate in batteries expands somewhat during discharge, which is why nearly all batteries have separators, such as glass mat or paper that can be compressed.
Most industrial (fork lift) deep-cycle batteries use Lead-Antimony plates rather than the Lead-Calcium used in AGM or gelled deep-cycle batteries and in automotive starting batteries. The Antimony increases plate life and strength, but increases gassing and water loss. This is why most industrial batteries have to be checked often for water level if you do not have Hydrocaps. The self discharge of batteries with Lead-Antimony plates can be high - as much as 1% per day on an older battery. A new AGM typically self-discharges at about 1-2% per month, while an old one may be as much as 2% per week.
Hydrocaps catalytically recombine the hydrogen and oxygen gases into pure water and return it to the cell. This reduces watering and washes the electrolyte spray back into the battery extending its useful power. The danger of hydrogen gas explosion is virtually eliminated and corrosion is stopped because the acid spray and fumes are contained.
To fully charge any storage battery a certain amount of overcharge is necessary. This overcharging equalizes the power in the cells of the battery. As each cell reaches 80% of capacity it dissipates the surplus energy by boiling. This causes the water in the electrolyte to separate into hydrogen and oxygen gases which vent from the battery and reduce the electrolyte level. Distilled water must be added to make up the loss or your battery could be ruined.
Simply replace the batteries standard vent caps with Hydrocaps for reduced battery maintenance
Sealed batteries are made with vents that (usually) cannot be removed. The so-called Maintenance Free batteries are also sealed, but are not usually leak proof. Sealed batteries are not totally sealed, as they must allow gas to vent during charging. If overcharged too many times, some of these batteries can lose enough water that they will die before their time.
Smaller deep cycle batteries (including AGM) use Lead-Calcium plates for increased life, while most industrial and forklift batteries use Lead-Antimony for greater plate strength to withstand shock and vibration. Lead-Antimony (such as forklift and floor scrubber) batteries have a much higher self-discharge rate (2-10% per week) than Lead or Lead-Calcium (1-5% per month), but the Antimony improves the mechanical strength of the plates, which is an important factor in electric vehicles. They are generally used where they are under constant or very frequent charge/discharge cycles, such as forklifts and floor sweepers. The Antimony increases plate life at the expense of higher self discharge. If left for long periods unused, these should be trickle charged to avoid damage from sulfation - but this applies to ANY battery. As in all things, there are tradeoffs. The Lead-Antimony types have a very long lifespan, but higher self discharge rates.
Batteries come in all different sizes. Many have "group" sizes, which is based upon the physical size and terminal placement. It is NOT a measure of battery capacity. Typical BCI codes are group U1, 24, 27, and 31. Industrial batteries are usually designated by a part number such as "FS" for floor sweeper, or "GC" for golf cart. Many batteries follow no particular code, and are just manufacturer’s part numbers. Other standard size codes are 4D & 8D, large industrial batteries, commonly used in solar electric systems.
U1 (12 volt) 34 to 40 AMP hours; Group 24 (12 volts) 70-85 Amp hours; Group 27 (12 volts) 85-105 Amp hours; Group 31 (12 volts) 95-125 Amp hour; 4-D (12 volts) 180-215 Amp hour; 8-D (12 volts) 225-255 Amp hour; Golf Cart & T-105 (6 volts) 180-225 Amp hour; and L-16, L16HC, etc (6 volts) 340 to 415 Amp hour.
Gelled batteries or "Gel Cells" contain acid that has been "gelled" by the addition of Silica Gel, turning the acid into a solid mass that looks like gooey Jell-O. The advantage of these batteries is that it is impossible to spill acid even if they are broken. The disadvantages are that they cannot be fast charged on a conventional automotive charger and they must be charged at a lower voltage or they may be permanently damaged. If a generator or inverter bulk charger is used, current must be limited to the manufacturer’s specifications. Better inverters commonly used in solar electric systems can be set to limit charging current to the batteries. If overcharged, voids can develop in the gel which will never heal, causing a loss in battery capacity. In hot climates, water loss can cause premature battery death. The newer AGM (absorbed glass mat) batteries have all the of gelled batteries advantages, with none of the disadvantages.
A newer type of sealed battery uses "Absorbed Glass Mats", or AGM between the plates. This is a very fine fiber Boron-Silicate glass mat. These type of batteries have all the advantages of gelled, but can take much more abuse. AGM batteries are also called "starved electrolyte", as the mat is about 95% saturated rather than fully soaked. That also means that they will not leak acid even if broken.
Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. They are non-hazardous so shipping costs are lower. They are practically immune from freezing damage since there is no liquid to freeze and expand, Most AGM batteries are "recombinant" (Oxygen and Hydrogen recombine inside the battery). They prevent the loss of water through electrolysis. Since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. AGM's have a very low self-discharge so they can sit in storage for much longer periods without charging than standard batteries. AGM's do not have any liquid to spill, and even under severe overcharge conditions hydrogen emission is far below the 4% max specified for aircraft and enclosed spaces. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.
Even with all the advantages of the AGM batteries, there is still a place for the standard flooded deep cycle battery. AGM's will cost about 1.5 to 2 times as much as flooded batteries of the same capacity. In many installations, where the batteries are set in an area where you don't have to worry about fumes or leakage, a standard or industrial deep cycle is a better economic choice. AGM batteries main advantages are no maintenance, completely sealed against fumes, Hydrogen, or leakage, non-spilling even if they are broken, and can survive most freezes. Not everyone needs these features.
Thermal mass means that because batteries have so much mass, they will change internal temperature much slower than the surrounding air temperature. A large insulated battery bank may vary as little as 10 degrees over 24 hours internally, even though the air temperature varies from 20 to 70 degrees.
Battery capacity is higher at high temperatures but battery life is shortened. Battery capacity is reduced by 50% at -22 degrees F - but battery LIFE increases by about 60%. Battery life is reduced at higher temperatures - for every 15 degrees F over 77, battery life is cut in half. This holds true for ANY type of Lead-Acid battery, whether sealed, gelled, AGM, industrial or whatever. The battery will tend to average out the good and bad times.
All Lead-Acid batteries supply about 2.14 volts per cell (12.6 to 12.8 for a 12 volt battery) when fully charged.
Batteries that are stored for long periods will eventually lose all their charge. This "leakage" or self discharge varies considerably with battery type, age, and temperature. It can range from about 1% to 15% per month. Generally, new AGM batteries have the lowest, and old industrial (Lead-Antimony plates) are the highest. In systems that are continually connected to some type charging source, whether it is solar, wind, or an AC powered charger this is seldom a problem.
The biggest killers of batteries are sitting stored in a partly discharged state for a few months. A "float" trickle charge should be maintained on the batteries even if they are not used. Even most "dry charged" batteries (those sold without electrolyte so they can be shipped more easily, with acid added later) will deteriorate over time. Maximum storage life on those is about 18 to 30 months. Batteries self-discharge faster at higher temperatures
A battery can meet the voltage tests for being at full charge, yet be much lower than it's original capacity. If plates are damaged, sulfated, or partially gone from long use, the battery may give the appearance of being fully charged, but in reality acts like a battery of much smaller size. This same thing can occur in gelled cells if they are overcharged and gaps or bubbles occur in the gel. What is left of the plates may be fully functional, but with only 20% of the plates left
All deep cycle batteries are rated in amp-hours.
An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH. The generally accepted AH rating time period for batteries used in solar electric and backup power systems (and for nearly all deep cycle batteries) is the "20 hour rate This means that it is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours it supplies is measured. Sometimes ratings at the 6 hour rate and 100 hour rate are also given for comparison and for different applications. The 6-hour rate is often used for industrial batteries, as that is a typical daily duty cycle. Sometimes the 100 hour rate is given just to make the battery look better than it really is, but it is also useful for figuring battery capacity for long-term backup amp-hour requirements. Why amp-hours are specified at a particular rate: Because of something called the Peukert Effect. The Peukert value is directly related to the internal resistance of the battery. The higher the internal resistance, the higher the losses while charging and discharging, especially at higher currents. This means that the faster a battery is discharged or used , the lower the AH capacity. Conversely, if it is drained slower, the AH capacity is higher. This is important because some manufacturers and vendors have chosen to rate their batteries at the 100 hour rate - which makes them look a lot better than they really are.
A battery is considered dead at 10.5 volts. At around 10.5 volts, the specific gravity of the acid in the battery gets so low that there is very little left that can do. In a dead battery, the specific gravity can fall below 1.1. How many stages should a deep cycle battery charger have? Deep cycle battery chargers (smart chargers) should have 3 basic stages: Bulk, Absorption, and Float. What is a bulk charge?
Current is sent to batteries at the maximum safe rate they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no "correct" voltage for bulk charging, but there may be limits on the maximum current that the battery and/or wiring can take.
Absorption Charge: Is the 2nd stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts. (The internal resistance gradually goes up because there is less and less to be converted back to normal full charge).
Float Charge: Is the 3rd stage of 3-stage battery charging. After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging.
In PWM, the controller or charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery. This may occur several hundred times per minute. It is called "pulse width" because the width of the pulses may vary from a few microseconds to several seconds. Note that for long term float service, such as backup power systems that are seldom discharged, the float voltage should be around 13.02 to 13.20 volts.
Standard and consumer chargers can “cook” the battery. Most garage and consumer (automotive) type battery chargers are bulk charge only, and have little, if any, voltage regulation. They are fine for a quick boost to low batteries, but not to leave on for long periods. A bulk charge will to bring the battery up cheaply. BUT... these chargers cause damage to the battery once the battery is fully charged.
A smart charger has 3 stages of charging (bulk, absorption and float). Bulk charging works like an old fashioned charger. Once the batteries reach various states of charge (almost full and totally full), the smart charger accounts for this by changing the amps and voltage of the energy it is putting into the battery. Once fully charged, the "smart charger" or "three stage chargers" will taper off its power to the battery, resulting in a battery that is protected from over charging. If you have expensive deep cycle batteries it is well worth it to invest in a smart charger.
A charge controller is a regulator that goes between the solar panels and the batteries. Regulators for solar systems are designed to keep the batteries charged at peak without overcharging. Meters for Amps (from the panels) and battery Most of the modern controllers have automatic or manual equalization built in, and many have a load output. There is no "best" controller for all applications - some systems may need the bells and whistles of the more expensive controls, others may not. Should I had acid the the battery? Never add acid to a battery except to replace spilled liquid. Distilled or demonized water should be used to top off non-sealed batteries.
The maintenance requirements change as the battery age. Older batteries will require longer charging time and/or higher finish rate (higher amperage at the end of the charge). Usually older batteries need to be watered more often. And, their capacity decreases while the self-discharge rate increases.
Nearly all batteries will not reach full capacity until cycled 10-30 times. A brand new battery will have a capacity of about 5-10% less than the rated capacity.
Batteries should be watered after charging if the plates are exposed, then add just enough water to cover the plates. After a full charge, the water level should be even in all cells and usually 1/4" to 1/2" below the bottom of the fill well in the cell (depends on battery size and type).
In situations where multiple batteries are connected in series, parallel or series/parallel, replacement batteries should be the same size, type and manufacturer if possible. Age and usage level should be the same as the companion batteries. Do not put a new battery in a pack which is more than 6 months old or has more than 75 cycles. Either replace with all new or use a good used battery.
The vent caps on flooded batteries should remain on the battery while charging. This prevents a lot of the water loss and splashing that may occur when they are bubbling. When you first buy a new set of flooded (wet) batteries, you should fully charge and equalize them, and then take a hydrometer reading for future reference. Since not all batteries have exactly the same acid strength, this will give you a baseline for future readings.
Lead-Acid batteries do not have a memory, and the rumor that they should be fully discharged to avoid this "memory" is totally false and will lead to early battery failure.
Inactivity can be extremely harmful to a battery. It is a very bad idea to buy new batteries and "save" them for later. Either buy them when you need them, or keep them on a continual trickle charge. The best thing - if you buy them, use them.
Do not use solvents or spray cleaners. Only clean water should be used for cleaning the outside of batteries.
A solution of baking soda and water can be used for cleaning the battery. Use one tablespoon of baking soda per cup of water until completely dissolved. It will neutralize and remove accumulations of acid contaminated soil on the battery and also cleanse the exterior. Do not allow the baking soda water to get in the battery; it is for external cleaning only. The baking soda solution should be rinsed away with plenty of clean water and then all surfaces dried.
Batteries that are in good condition and fully charged will have a resting voltage of around 12.6 volts. As they are used to power items the voltage will drop as the battery gives up some of its energy. Eventually, the battery will be "dead" and will need recharging. Note that a fully dead battery has 10.5 volts of resting charge. However, the minute you apply a load to it, the voltage plummets and nothing happens. Just remember that 12 volt batteries are not full at 12 volts and dead at zero. They are dead at 10.5 and fully charged at 12.6.
Flooded batteries are filled with electrolyte. This electrolyte changes in density according to the state of charge. A fully charged battery will have a high acid content which gives it a higher specific gravity. A discharged battery will be pretty much water, which has a lower density. This density, commonly referred to as Specific Gravity, can be measured with either a hydrometer or spectrometer. The advantage of this method, rather than just checking for battery voltage, is that each cell can be tested. A voltmeter can only give you an average output level across all of the battery cells while a hydrometer will show you if a single cell is bad. Note that a hydrometer test only applies to flooded batteries, not AGM batteries.
A battery hydrometer is an instrument that checks the charge of a battery by measuring the density of the electrolyte in the cells. A hydrometer reading gives a valuable first indication that there may be a charging-system failure. A battery hydrometer consists of a rubber squeeze bulb, a float chamber, and an accurately weighted float. The amount of sulfuric acid in a lead-acid battery indicates the state of charge. The greater the concentration of acid in the electrolyte, the denser the electrolyte and the greater the level of charge.
Water has a specific gravity (SG) of 1.000; sulfuric acid has an S.G. of 1.830. Each cell in a fully-charged battery has an SG in the range 1.240 to 1.280. The electrolyte in a totally discharged battery has a specific gravity of about 1.100. Specific gravity falls with increasing temperature.
To use a battery hydrometer draw enough electrolyte into the device to set the float adrift, without it touching the sides. Sight across the main level and ignore the meniscus that rises up the sides of the instrument.
Use a voltmeter to check the battery as follow: 12.6 + volts, 100% state of charge; 12.5 + volts, 90% state of charge; 12.42 + volts, 80% state of charge; 12.32 + volts, 70% state of charge; 12.20 + volts, 60% state of charge; 12.06 + volts, 50% state of charge; 11.9 + volts, 40% state of charge; 11.75 + volts, 30% state of charge; 11.58 + volts, 20% state of charge; 11.31 + volts, 10% state of charge; 10.5 + volts, 0% state of charge (dead). . A voltmeter can only gives you an average output level across all of the battery cells.
Yes, you can use a battery tester to determine the level of charge. Never short across the posts of a battery to determine its level of charge. Even a heavily discharged battery can produce a spark that could ignite hydrogen gas around the battery and cause an explosion. Connecting the two posts of a battery with a short wire may also cause burns to the hands.
Undercharging and overcharging a battery.
Generally it is caused by not allowing the charger to restore the battery to full state of charge after use. Continually operating the battery in a partial state of charge, or storing the battery in a discharged state result in the formation of lead sulfate compounds on the plates. This condition is known as sulfation. Both of these conditions reduce the battery's performance and may cause premature battery failure. Undercharging will also cause stratification.
Continuous charging causes accelerated corrosion of the positive plates, excessive water consumption, and in some cases, damaging temperatures within a lead acid battery. Deep cycle batteries should be charged after each discharge of more than 50% of the batteries rated capacity, and/or after prolonged storage of 30 days or more.
Always keep the level of the electrolyte at the proper level. Add distilled water to raise the electrolyte level. Add water to a discharged battery only when it is about to be recharged. Batteries should be kept clean and dry. Moist accumulations of dirt on a battery may cause it to lose its charge due to current flowing through the moist dirt from one post to the other. Battery connections should be dry, clean, shiny, and snug fitting, but not so tight that they must be forced together by hammering or severe twisting. The battery should be held in place with clamps or other restraints. Vibration or bouncing is hard on cable connections, the battery case and internal parts, and will shorten the life of the battery.
A frequent need to add water may indicate that the battery is being overcharged, so the vehicle's charging system should be checked. Maintenance free batteries are sealed, resulting in electrolyte levels which can't be adjusted, although there are vents for gases to pass through.
Virtually all boats under 40 feet or so that have an electrical system operate at a nominal voltage of 12 volts. That is, they use a battery that has a fully-charged potential of 12.6 volts, and the loads and charge devices that are installed on the boat are designed to operate between roughly 12 and 14 volts.
The main reason is that boats use automotive and industrial components which are also based on a 12 volt standard. Do larger boats use 12 volts electrical systems? As boats get larger, in the 50-60 foot range, the DC loads are greater, the wire runs longer so 12 volt systems become inadequate or at least challenged. That’s because it becomes increasingly difficult to avoid voltage drop—the nemesis of boat wiring systems—which can make electrical devices function less efficiently. Voltage drop occurs due to the electrical resistance in wires, connectors, switches, and other conductors in an electrical circuit. No component is immune from contributing to this plague, but voltage drop can be measured and managed, and correctly-engineered boats don’t usually suffer from it.
A 240 watt bilge pumping a 24 volt system will draw half the amps as in a 12 volt system so a smaller wire can be used to carry the load. The resulting smaller wire has several advantages: It’s less expensive (going down three sizes of wire generally saves 50-70% of the cost of wire.) ; It’s lighter, so your boat is more efficient.; and It’s smaller, so it’s easier to run in tight spaces and around corners.
The main reason is that so many more products are available in 12V versions, especially pumps, electronics, inverters and chargers. 12V systems require a single battery to operate. 24V systems require two 12V batteries in series, which increases the weight and volume of the battery bank. The advantage of using smaller wire is only realized when the currents are large or the wire runs are long. Small boats can use 16 Gauge wires for most of their circuits and stay within ABYC limits. Most vessel electrical systems begin with an engine (or two) with its starter, alternator, engine instruments, starter solenoid, possible fuel injection system, and so forth. The vast majority of engines designed for pleasure boats are 12V-based, making it very difficult to eliminate a 12V system from your boat. Can I run 12 volt equipment from my 24 volt electrical system??Yes you can…… Use a 24V to 12V converter that can power your 12V products. This might be a very small (10A) device to power a single electronic item, like a VHF radio, or it could be a large converter (50-100A) which would power many systems throughout the boat. As power consumption for electronics increases (a SSB draws 30A at 12V when transmitting), this option can require larger converters, which may not be electrically “quiet” and thus may interfere with the very loads they are powering. All DC to DC power converters should be listed as FCC “Class B”, meaning that they produce very little interference.
You can install both a 12V and a 24V system in the boat. This generally requires two alternators, two battery banks, two distribution panels (or two delineated areas of a single distribution panel), and two battery monitoring systems. Dual voltages may reduce the redundancy in the vessel systems if one battery bank fails.
The alternator of a given frame size (and heat load) will put out the same current at 24V as it will at 12V (it is basically a current-source), which means twice the power from the same-sized unit. So a single large-frame 24V alternator will easily charge a house bank and run a large DC compressor and water maker, where it would be a struggle with 12V.”

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