A few systems use NiCad, but we do not recommend them except in cases where extremely cold temperatures (-50 F or less) are common. Eds blog posts appear courtesy of his website, EdsBoatTips. Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. How to Buy a Boat: Tips for a First Time Buyer, Top 10 New Fishing Boats for Under $20,000, What Type is Right for You? Lifespan is increased at the same rate if below 77 degrees, but capacity is reduced. Regulators for solar systems are designed to keep the batteries charged at peak without overcharging. At approximately -22 degrees F (-27 C), battery AH capacity drops to 50%. While plate thickness is not the only factor in how many deep cycles a battery can take before it dies, it is the most important one. that it is almost impossible to give a fixed number. This is a very fine fiber Boron-Silicate glass mat. Even though battery capacity at high temperatures is higher, battery life is shortened. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. Throughout this FAQ, we have stated that a battery is considered dead at 10.5 volts. One major disadvantage is that there is a large voltage difference between the fully charged and discharged state. Voltages at this stage typically range from 10.5 volts to 15 volts. Inactivity can be extremely harmful to a battery. This also means that since they are non-hazardous, the shipping costs are lower. They are generally used where they are under constant or very frequent charge/discharge cycles, such as fork lifts and floor sweepers. Obviously, there are some practical limitations on this - you don't usually want to have a 5 ton pile of batteries sitting there just to reduce the DOD. Photo courtesy of ProSport. 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". Absorption Charge: The 2nd stage of 3-stage battery charging. Here are two worked examples using our 100 Ah battery from above (that we have increased to 120 Ah so as to reduce wear and tear from very deep cycling). We need to learn a bit about amp-hour ratings for thingslike alternators and battery chargers, and about how to size a battery bank to keep all your gearrunning at its peak performance for as long as you need it to.Starting Batteries and Battery RatingsIts important to understand the different ratings used to determine battery capacity andalso to understand that sometimes battery manufacturers will use specifications thatmay do more to confuse you than actually help in making the right choices. The Antimony increases plate life at the expense of higher self discharge. There is little you can do to check these issues and so buying second hand can be risky. (There are some NiCads in use, but for most purposes the very high initial expense, and the high expense of disposal, does not justify them). It is lead acid batteries than can be cranking (designed to deliver short bursts of high energy) or deep cycle. Starting batteries have a large number of thin plates for maximum surface area. If you look at the fine print, it has that rating only at 5% DOD - it is much less when used in an application where they are cycled deeper on a regular basis. This is not usually a problem with solar electric systems, but if an auxiliary generator or inverter bulk charger is used, current must be limited to the manufacturers specifications. VPC is the volts per individual cell - if you measure more than a .2 volt difference between each cell, you need to equalize, or your batteries are going bad, or they may be sulfated. The vent caps on flooded batteries should remain on the battery while charging. In general, you get what you pay for. Practically all batteries used in PV and all but the smallest backup systems are Lead-Acid type batteries. This is true of flooded lead acid and sealed lead acid batteries. In PWM, the controller or charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery. Many inverters and charge controls have a hard time with them. 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. Solvents or spray cleaners should not be used. Unfortunately, it is not possible to open up batteries and measure plate thickness, but there are two giveaways: When it comes to purchasing a deep cycle battery, this is one of those times when purchasing a well recognized brand is well worth the slightly higher cost. At higher temperatures (over 85 degrees F) this should be reduced to about 2.10 volts per cell. The links below are on this page - you can also just scroll down if you want to read them all. They are expensive to buy and very expensive to dispose of due to the hazardous nature of Cadmium. Most of the modern controllers have automatic or manual equalization built in, and many have a LOAD output. Copyright 2022 Northern Arizona Wind & Sun. However, NiCads can be frozen without damage, so are sometimes used in areas where the temperatures may fall below -50 degrees F. Most AGM batteries will also survive freezing with no problems, even though the output when frozen will be little or nothing. For longest life, batteries should stay in the green zone. Conversely the lower the drain, the more efficient the battery is. Batteries that are being charged will be higher - the voltages while under charge will not tell you anything, you have to let the battery sit for a while. STEP ONE: Make sure it really is a deep cycle battery, STEP TWO: Understanding the amp hour rating, STEP THREE: Understanding the depth of discharge cycles, Video of What makes a Deep Cycle Battery Different with Transcript, VIDEO What makes a deep cycle battery different, VIDEO How a flooded lead acid battery is made. This tends to even out in most systems - they will spend part of their life at higher temperatures, and part at lower. Float voltage for Lead-Acid batteries should be about 2.15 to 2.23 volts per cell, or about 12.9-13.4 volts for a 12 volt battery. For a 220 AH battery, this would equal 26 Amps.) Deep Cycle Battery as a Starting Battery? (Some, such as the Concorde AGM, use the 24 hour rate, which is probably a better real-world rating). The sensor will then read very close to the actual internal battery temperature. As in all things, there are trade offs. To properly check the voltages, the battery should sit at rest for a few hours, or you should put a small load on it, such as a small automotive bulb, for a few minutes. Either replace with all new or use a good used battery. Xantrex Morningstar Midnite Solar Outback Power Steca You can find all these brands, as well as others, in our charge controller section. All AGM & gelled are sealed and are "valve regulated", which means that a tiny valve keeps a slight positive pressure. Batteries should be wateredaftercharging unless the plates are exposed, then add just enough water to cover the plates. And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. Among the regulated chargers, there are the voltage regulated ones, such as Iota Engineering, PowerMax, and others, which keep a constant regulated voltage on the batteries. Deep Cycle Battery as a Starting Battery. 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. A battery rated at 180 amp-hours over 6 hours might be rated at 220 AH at the 20-hour rate, and 260 AH at the 48-hour rate. Hydrometer readings may not tell the whole story, as it takes a while for the acid to get mixed up in wet cells. The major construction types are flooded (wet), gelled, and sealed AGM (Absorbed Glass Mat). This has allowed some less reputable manufacturers to label starter batteries as deep cycle especially in the lead acid battery arena. The Peukert value is directly related to the internal resistance of the battery. Concorde and some other AGMbatteries are a special case - they can be charged at up the the Cx4 rate, or 400% of the capacity for the bulk charge cycle for a short period. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. A newer type of sealed battery uses "Absorbed Glass Mats", or AGM between the plates. Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. Modern battery technology can mean a higher acceptance rate for charging, which in turn means that buying a higher-output charger might be a smart decision. The Lead-Antimony types have a very long lifespan, but higher self discharge rates. It can vary to extremes - we have seen L-16's killed in less than a year by severe overcharging and water loss, and we have a large set of surplus telephone batteries that see only occasional (10-15 times per year) heavy service that was just replaced after 35+ years. We have seen golf cart batteries destroyed without ever being used in less than a year because they were left sitting in a hot garage or warehouse without being charged. Many have "group" sizes, which is based upon the physical size and terminal placement. Plate thickness (of the Positive plate) matters because of a factor called "positive grid corrosion". In rechargeable batteries, this process can be repeated many times. 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. Because of something called thePeukert Effect. Connected to a 100 Amp appliance, the same battery might only last a matter of minutes. Because of this characteristic, you have to be on the lookout for under handed manufacturers who might try to pull the wool over your eyes. This is a charge that is about 10% higher than normal full charge voltage, and is applied for about 2 to 16 hours. Starting (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Most better inverters commonly used in solar electric systems can be set to limit charging current to the batteries. 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. A battery can meet the voltage tests for being at full charge, yet be much lower than it's original capacity. A battery "cycle" is one complete discharge and recharge cycle. 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 major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. So a 100Ah battery should power a 100 Amp appliance for one hour . Here well cover the steps you can follow to find the right battery for your needs. We have seen gelled cells destroyed in one day when overcharged with a large automotive charger. Note that forlong termfloat service, such as backup power systems that are seldom discharged, the float voltage should be around 13.02 to 13.20 volts. Another problem is that they are very inefficient - you lose anywhere from 30 to 40% in heat just by charging and discharging them. It is sometimes hard to tell, as the term deep cycle is often overused - we have even seen the term "deep cycle" used in automotive starting battery advertising. Sometimes ratings at the6 hour rateand100 hour rateare also given for comparison and for different applications. State of charge, or conversely, the depth of discharge (DOD) can be determined by measuring the voltage and/or the specific gravity of the acid with a hydrometer. If you are investing for the long term and you would like your battery to get the most from your purchase then one with an Ah rating twice that which you actually require would give you a much better service life and actually represent a cost saving. 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. Sealed batteries are made with vents that (usually) cannot be removed. The voltages below apply to ALL Lead-Acid batteries, except gelled. This is why your car battery dies on a cold winter morning, even though it worked fine the previous afternoon. Some charge controls have temperature compensation built in (such as Morningstar) - this works fine if the controller is subject to the same temperatures as the batteries. We learned how to recognizea real deep cycle battery and not a mislabeled starter battery, We checked the discharge rating used by the manufacturer to arrive at their Amp Hour rating, where we determined a 100 Ampere Hour battery (at the 20 hour rating) would power our 5 Amp appliance for the required 20 hours. Deep cycle batteries have much thicker plates than automotive batteries. AGM batteries are also sometimes called "starved electrolyte" or "dry"because the fiberglass mat is only 95% saturated with Sulfuric acid and there is no excess liquid. Starter batteries use less lead (the main cost in the production process) because the plates in the cell are thinner. There is a great deal of misunderstanding that surrounds deep cycle batteries, which often leads to extra costs as buyers follow false economies. Nearly all batteries will not reach full capacity until cycled 10-30 times. Solar Pump Controllers & Current Boosters, Solar Pump Installation Equipment & Accessories, Pump Installation Equipment & Accessories. Some other disadvantages of gel cells is that they must be charged at a lower voltage (2/10th's less) than flooded or AGM batteries. Once the charging voltage reaches 2.583 volts per cell, charging should stop or be reduced to a trickle charge. Conversely, if it is drained slower, the AH capacity is higher. This deep-cycle marine/RV battery is rated for 500 MCA (marine cranking amps) and 80 amp-hours. This ranks among the top 3 reasons for battery failure. In a dead battery, the specific gravity can fall below 1.1. Flooded battery life can be extended if anequalizing chargeis applied every 10 to 40 days. It is NOT a measure of battery capacity. Also, there is an upper limit - a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. Deep-cycle includes solar electric (PV), backup power, traction, and RV and boat "house" batteries. A brand new battery will have a capacity of about 5-10% less than the rated capacity. This prevents a lot of the water loss and splashing that may occur when they are bubbling. Voltages at this stage are typically around 14.2 to 15.5 volts. This is actually not as bad as it seems, as the battery will tend to average out the good and bad times. This is why most industrial batteries have to be checked often for water level if you do not have Hydrocaps. 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. when the surrounding temperature is regularly around freezing point, the performance drops by 20% so a 120 Ah battery is actually a 95 Ah battery (120 Ah x 80%). This makes sure that all the cells are equally charged, and the gas bubbles mix the electrolyte. The best determination is to measure the specific gravity, but in many batteries this is difficult or impossible. What you save on batteries you will have to make up for by buying a larger solar panel system. If your deep cycle battery is going to experience colder conditions, it is better to up the capacity in order to achieve the performance you expect. However, there are often ratings for other depth of discharge cycles, the most common ones are 10%, 20%, and 50%. It is called "pulse width" because the width of the pulses may vary from a few microseconds to several seconds. This means that they can sit in storage for much longer periods without charging than standard batteries. Max storage life on those is about 18 to 30 months. It is usually considered to be discharging from 100% to 20%, and then back to 100%. 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. The battery may short out or it will just last for shorter and shorter periods requiring a replacement purchase long before it should be necessary. Batteries are divided in two ways, by application (what they are used for) and construction (how they are built). Should I upgrade to a Gel Battery for my trolling motor? 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. (Video of What makes a Deep Cycle Battery Different with Transcript). For example, one of the widely advertised telephone type (float service) batteries have been advertised as having a 20-year life. A clamp-on meter set to measure amperes will help you determine the electrical demands of your system. If these are set to the correct voltages for your batteries, they will keep the batteries charged without damage. The standard rating for batteries is at room temperature - 25 degrees C (about 77 F). That also means that they will not leak acid even if broken. Marine batteriess are usually a "hybrid", and fall between the starting and deep-cycle batteries, though a few (Rolls-Surrette and Concorde, for example) are true deep cycle. Automotive batteries typically have plates about .040" (4/100") thick, while forklift batteries may have plates more than 1/4" (.265" for example in larger Rolls-Surrette) thick - almost 7 times as thick as auto batteries. Only clean water should be used for cleaning the outside of batteries. 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. This gives less surface area, thus less "instant" power like starting batteries need. Those same batteries are rated at less than 5 years if cycled to 50%. The Concorde batteries can be almost fully recharged (95% or better) even after 30 days of being totally discharged. To make an accurate assessment of your boat's requirements for both mission-critical and less important demands, use a load requirements worksheet like this example from the American Boat and Yacht Council. NiCads are also inefficient - typically around 65% - and very expensive. 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. Voltage on a fully charged battery will read 2.12 to 2.15 volts per cell, or 12.7 volts for a 12 volt battery. Not everyone needs these features. A charge controller is a regulator that goes between the solar panels and the batteries. NiFe (Nickel-Iron) batteries are also available - these have a very long life, but rather poor efficiency (60-70%) and the voltages are different, making it more difficult to match up with standard 12v/24/48v systems and inverters. You might be thinking I have a 5 Amp appliance that I need to power for 20 hours, so what I need is a 100 Ah battery that was defined as such using the 20 hour rate. Click on the small graph to see a full size chart of temperature vs capacity. We have used the Concorde SunXtender AGM batteries in some of our vehicles with no problems. This is why we recommend the charge controls and battery chargers listed in the sections above. The correct term is deep cycle. It can range from about 1% to 15% per month. Engine starters need a very large starting current for a very short time. go to our Batteries for Deep Cycle Applications page. And, their capacity decreases while the self-discharge rate increases. In the past they were often used by railroads as backup power, but nearly all have now changed over to newer types. However, since very few battery cables can take that much current, we don't recommend you try this at home. (The internal resistance gradually goes up because there is less and less to be converted back to normal full charge). It will vary from about 2.74 volts per cell (16.4 volts) at -40 C to 2.3 volts per cell (13.8 volts) at 50 C. This is why you should have temperature compensation on your charger or charge control if your batteries are outside and/or subject to wide temperature variations. Usually older batteries need to be watered more often. Note the large voltage drop in the last 10%. In leisure applications, this is often inevitable yachts, for example, can be cold, especially at night when far from shore and this is the exact time the battery is needed. At 50% the reading will be 2.03 VPC (Volts Per Cell), and at 0% will be 1.75 VPC or less. These use a variable voltage to keep the charging amps much more constant for faster charging. Note that the voltages whenactually chargingwill be quite different, so do not use these numbers for a battery that is under charge. This does not apply to gelled or AGM 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). For gel cells, subtract .2 volts. There are so many variables, such as depth of discharge, maintenance, temperature, how often and how deep cycled, etc. The recombining is typically 99+% efficient, so almost no water is lost. Understand the demands of your on-board electrical equipment, and assess the abilities of your batteries and charging gear to keep up with those demands. 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. Slower charging and discharging rates are more efficient. They are sometimes used in larger PV systems because you can get a lot of storage in a single (very large and heavy) battery. The higher the rate of discharge, the higher the internal resistance inside the cells and the more energy that is wasted in heat. Battery life is directly related to how deep the battery is cycled each time. The best thing - if you buy them, use them. Batteries come in all different sizes. As a general rule, if you are going to use a true deep cycle battery (such as the Concorde SunXtender) also as a starting battery, it should be oversized about 20% compared to the existing or recommended starting battery group size to get the same cranking amps. We can see this by using a formula known as Peukerts Law: You can work out your own needs using our online Peukerts Law calculator. For the purposes of this article however well stick with 120Ah. A "float" trickle charge should be maintained on the batteries even if they are not used (or, especially if they are not used). You can have very strong solution at the bottom, and very weak at the top of the cell. He also is the curriculum director for the American Boat and Yacht Council. They cannot be fast charged on a conventional automotive charger or they may be permanently damaged. When using a small solar panel to keep afloat (maintenance) charge on a battery (without using a charge controller), choose a panel that will give a maximum output of about 1/300th to 1/1000th of the amp-hour capacity. The one issue that Peukerts Law (see above) does not take into account is temperature, it assumes temperature will be around 77F (25C). Unfortunately, battery performance significantly declines in colder conditions. Starting batteries are usually rated at "CCA", or cold cranking amps, or "MCA", Marine cranking amps - the same as "CA". This same thing can occur in gelled cells if they are overcharged and gaps or bubbles occur in the gel. Bear in mind that installing a new high-output alternator on an older engine will probably require other modifications, too. We stock all of theIota Engineeringbattery chargers. An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. Gelled cellsshould be charged at no more than the C/20 rate, or 5% of their amp-hour capacity. Trojan T-105 = 1.25; Optima 750S = 1.109; US Battery 2200 = 1.20. For the best experience on our site, be sure to turn on Javascript in your browser. How fast can a Sealed Lead Acid rechargeable battery charge? With stratification, you can test a battery with a hydrometer and get readings that are quite a ways off. The subject of batteries could take up many pages. For a very brief discussion on the advantages and disadvantages of these and other types of batteries, such as NiCad, NiFe (Nickel-Iron), etc. Battery life is reduced at higher temperatures - for every 15 degrees F over 77, battery life is cut in half. Flooded may be standard, with removable caps, or the so-called "maintenance free" (that means they are designed to die one week after the warranty runs out). These are usually special purpose "float service", but often appear on the surplus market as "deep cycle". The 140-minute reserve capacity indicates the number of minutes a battery can deliver 25 amps of current without dropping below 10.5 volts. Distilled or deionized water should be used to top off non-sealed batteries. There is generally no problem with this, providing that allowance is made for the lower cranking amps compared to a similar size starting battery. All deep cycle batteries are rated in amp-hours. Fortress Power and Victron Energy Webinar, Electronics Guru Goes Off-Grid with Solar in Baja, Mexico, Alaska Off-Grid Resident Harnesses Energy from the Sun, Northern Utah Residents Outfit Shelter with Solar Power, Couple Converts School Bus into Solar Powered Skooly, Rolls-Surrette premium deep cycle: 7-15 years. Battery capacity is reduced by 50% at -22 degrees F - but battery LIFE increases by about 60%.
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