THE BASICS ON BATTERIES Show First things first. A 12-volt battery is not a 12-volt battery. Twelve volts is just a nominal, convenient term used to distinguish one battery from another. A fully-charged 12-volt battery, allowed to “rest” for a few hours (or days) with no load being drawn from it (or charge going to it), will balance out its charge and measure about 12.6 volts between terminals. When a battery reads only 12 volts under the above conditions, it’s almost fully depleted. Actually, if a battery’s resting voltage is only 12.0 to 12.1 it means only 20 to 25% of its useful energy remains. It’s either a goner or it has been deep cycled, and a battery can only be deep-cycled a limited number of times before it is indeed dead. 12-volt batteries supply useful energy only through a limited range — from over 14 volts (when fully charged and unrested) down to 10.5 volts in use/under load (when lights dim, pumps groan and TV pictures get small). No 12-volt battery will remain at over 14 volts for more than seconds unless it’s being charged. The lowest limit is 10.5 volts (used in testing) and obviously unsatisfactory in practical use. Experienced RVers try to use no more than 20% to 50% of the energy available in a battery before recharging. That means they never let resting voltage get below 12.5. They never use more than 50% before recharging (resting volts of 12.3) except in an emergency. They know that, if resting voltage ever reaches 12.1, they have deep-discharged one cycle and that a battery is good for only so many cycles (from as low as 20 in an automotive battery to 180 in a golf cart battery, with the typical RV/marine battery good for no more than 30). Watts = Volts x Amps example: 60W = 12V x A and 60 ÷ 12 = 5 amps BATTERY CHARGING VOLTAGE You have to have more “juice” at one end of a wire than you need at the output or electricity won’t flow. The wire you pump electricity through and the connections in the lines resist the flow. You have to overpower it. Similarly, batteries have an inherent resistance to take a charge because of their chemical makeup. You have to force more electricity into a battery than it would like to accept or it won’t be fully charged. To charge a standard 12-volt battery, you have to bring it up to above 14 volts (amount varies with the type of battery). When checking the batteries, (at rest) use these “Voltage Landmarks”. 12.6 volts = 100% The typical wet-cell battery (lead plates in a mixture of sulfuric acid and water) needs to be charged up to about 14.+ volts in order to adequately distribute those funny little things called electrons through the plates. Once that’s done, the battery can rest. As it does, the electrons distribute themselves and eventually balance out at 12.6 volts (more or less, depending on the type battery and its condition). This is your starting point. MORE AMPS AND VOLTS Look at voltage as two things: First, a force that pushes electrons — Second, as a handy measurement. Look at amperes as two things: First, a quantity of energy (like you would a gallon of gas) — Second, as a handy measurement. From a (nominal again, don’t forget) 12-volt tub of energy, you can extract just so many amperes of power. Keep in mind that the laws of physics prevent you from getting more out of something than you put into it! Keep in mind that waste (those wires, battery contents and such) prevents you from taking out as much as you put in. Keep in mind that you’re going to have to put in about 10% more electrical power than you use (high school physics). A battery bank is like a “money” bank or checking account — if you repeatedly take more out than you put in, you’ll eventually be in trouble. MORE ON BATTERY CHARGING Sustained charging, where the batteries are “floated” at a constant charge (as in the RV converter or with an automatic portable charger) should not be done at more than 13.8 volts (and 13.65 makes batteries last longer). It’s supposed to keep the batteries “up” to a reasonable level without undercharging or overcharging them (the assumption being
you’ll “top them off” by driving). Unfortunately, many cheap chargers and RV converters don’t regulate very well. Overcharging destroys batteries quickly. Undercharging destroys batteries too, but more subtly as the battery stratifies and will no longer maintain a charge. In effect, the 100 amp/hour RV battery becomes a 10 amp/hour battery after consistent undercharge. It will read full voltage, but as soon as a small load is placed on it, it drops to nothing. RVers who remain plugged into
commercial power for long periods often never know this has happened until they unplug, because the converter’s transformer also supplies power directly to the RV circuits while it’s charging the battery — or trying to. BATTERY EQUALIZING Follow safety precautions, use safety goggles, plenty of ventilation, etc. Some battery people recommend equalizing in this manner every three months (or after 5 deep cycles). I think the wear and tear on a 12V battery from equalizing this often does more damage than it’s worth. Batteries held at 13.8 or so for long periods get lazy and like it there. They need some “equalizing” also. Not as drastic as above, fortunately. If you drive occasionally, your engine alternator should do it (assuming the regulator is set properly). So will a solar electric system or a good, well-regulated independent battery charger. If nothing else, use the manual charger once in a while when parked and plugged in, but just bring volts up to 14.+ (whatever’s appropriate) and stop there. Golf Cart Battery BATTERY
CHARGE/DISCHARGE RATE BATTERY
TROUBLESHOOTING AND BATTERY TESTING Measuring, metering, testing and troubleshooting require only a few tools and basic knowledge. Much of it is common sense, requiring no tools. Do not ever depend on the red/yellow/green idiot meter installed in most RV’s. Get a digital meter. You need a digital meter to accurately read battery voltage to tenths of a volt. You should have an Analog (needle face) meter also. You can’t tell the difference between battery voltages with an analog with great accuracy, but they are better in some ways (because it’s easier to see rapid changes) than digital meters for reading fluctuations. (Much more later.) Get a 12-volt troubleshooting light/test lamp from any auto store cheap or make your own. (Meters will indicate voltage even if there’s only one strand left in a wire. Test lamps won’t light if there’s not enough wire to carry the load.) Get a decent hydrometer if you have wet-cell batteries and can remove the caps. Don’t get a cheapie with colored, floating balls. Learn how to read a hydrometer. Battery Testing
Specific Gravity: Full charge SG will run from about 1.260 in an auto battery to about 1.275 in a golf cart. High SG (more acid) allows more juice (current) to be drawn–but only up to a point; then the battery deteriorates–fast. Golf cart plates are made to handle this, RV/Marine somewhat, automotive not at all. Don’t try to get more AH by adding acid (or vinegar instead of distilled water), the battery will just die sooner. MORE
ON SPECIFIC GRAVITY–and checking resting voltage Look especially for differences between cells. A variation of .050 between any means a possible problem. This is after it’s charged and bubbled a bit to mix chemicals thoroughly. If it’s a new battery and this happens, take it back. If old, plan on replacing it soon. It probably has a stratified/shorted cell. Initially, there’s no need in checking SG until a battery reaches about 70% of full charge and is bubbling/gassing slightly (not boiling like a coffee pot). Then, take readings once each hour and write them down. When three successive readings are alike, the battery is as charged as it will get. Record readings for each cell and battery. Disconnect battery from any charge or load and leave it overnight (24 hours is better). Check SG again. Readings may be a bit lower, but should be consistent. Record these as your new baseline: your normal, full charge, resting values. Do this again after two weeks or a month of use. Readings may be slightly higher, but again, should be consistent. If the batteries have been constantly overcharged or undercharged, it will show up here. You should have checked that your battery charger was set properly before starting all this, but if you get abnormal readings check that your charger is regulating properly (see later). If you have to add water this soon, you are almost definitely overcharging. Once you’ve done the above tests, you shouldn’t have to do it more than twice a year unless you detect a problem. You should check water level about once a month. Ideally, you shouldn’t have to add water more than two to four times a year. More than that probably indicates overcharging. Using a Hydrometer Without Making a Mess Stick it in a cell until it just rests on top of the plates. Squirt in and out a few times–gently, don’t splatter. Then fill until the inner tube floats. Too little and it will rest on bottom of hydrometer. Too much and it will hit the top. In either case, you’ll get false readings. Don’t remove the thing from the cell to read it, you’ll just drip acid all over. Take your reading and write it down. Read at the fluid level, not at the slight curvature where the fluid touches the inner tube. (Before moving to the next cell, don’t forget to squirt the acid back in.) Note temperature on thermometer and correct reading as indicated. Note, again, that all readings for a battery should be within .050 of each other. Keep in mind you might have a cheap or faulty hydrometer. El cheapos have a paper SG scale in the tube that slips up and down. Load testing is yet another way of testing a battery. Load test removes amps from a battery much like starting an engine would. A load tester can be purchased at most auto parts stores. Some battery companies label their battery with the amp load for testing. This number is usually 1/2 of the CCA rating. For instance, a 500CCA battery would load test at 250 amps for 15 seconds. A load test can only be performed if the battery is near or at full charge. Hydrometer readings should not vary more than .05 differences between cells. Digital Voltmeters should read as the voltage is shown in this document. The sealed AGM and Gel-Cell battery voltage (full charged) will be slightly higher in the 12.8 to 12.9 ranges. If you have voltage readings in the 10.5 volts range on a charged battery, that typically indicates a shorted cell. If you have a maintenance free wet cell, the only ways to test are voltmeter and load test. Any of the maintenance free type batteries that have a built in hydrometer(black/green window) will tell you the condition of 1 cell of 6. You may get a good reading from 1 cell but have a problem with other cells in the battery. MAINTENANCE Maintenance is all-important. Crud on top of a battery provides a path between poles. It’s a “short.” One most people never notice, but it uses energy constantly.You don’t need to slop baking soda all over. Often just a spray ‘n wipe with household cleaner is all that’s needed.
MORE DETAILS ON BATTERIES (MOSTLY GEL CELLS and AGM) And here’s where the difference between gels, AGMs and regular, wet-cell batteries starts to show up seriously.
Pros and Cons: Standard, old-timey flooded batteries are cheap (initially). They’ll do the job (golf carts or similar better than RV/Marine stuff). See remarks elsewhere. They will vent gas and fluid, but it can be replenished with distilled water. They require a lot of care. Gells and AGMs can do a better job and last longer, BUT also require special care. They’re rather expensive initially (but my six gels are in their tenth year, as good as new, and the cost nets out to less than standard batteries). However, they are very carefully charged and that requires an expensive charger/regulator. Gels and AGMs don’t need a lot of maintenance and cleaning (other than a quick spray and wipe from a household cleaner) UNLESS you do something stupid and overcharge them. They won’t spill acid, are very shock resistant, don’t pass gas (pun intended) unless seriously overcharged, have a VERY low self-discharge rate (nice when the RV is in storage) and have a very long cycle life. I’ve used golf cart batteries, regular batteries and gels. As I’ll repeat with more detail elsewhere, golf carts and similar batteries are, all things considered, the best solution. Were I to have to replace my batteries today (they’re in the living compartment in a small RV), I’d go with AGM. In a bigger RV, I’d go with golf cart or fork lift batteries. You should never charge a gel battery to more than 14.1 volts (or to more than the voltage specified by the manufacturer) before the regulator shuts off the charger except for very brief periods. Then, as a battery is “floated” (kept on the charger with a charge applied to keep it up to a reasonable level), it should never exceed 13.8 volts (better, for long life is a maximum of 13.65 volts). Again, though, you don’t float the battery permanently. You occasionally bring it up to 14.+ (this is EZ with a solar regulator or better quality battery charger that will perform regulating tasks frequently and automatically. (more later.)AGMs are charged similarly, just with different voltages. Actually, you’d be foolish to keep (float) any battery at a sustained charge of over 14 volts. You’d just wear it out prematurely and it would be spewing acid all the time, making a mess. But with a regular, wet-cell battery with removable caps, you can add water and clean up the corrosion. With a gel, or any other (really) sealed battery, you can’t add water. All you can do is watch the battery deteriorate. Gel batteries and AGMs do have caps, but don’t ever try to remove them. First, you’ll violate the warranty. Second, you’ll contaminate the inside. When it dies early, the dealer/factory will know you did this and will void the warranty. Also, if you overcharge a gel or AGM battery, the factory can detect that, too. Again, no more warranty. TEMPERATURE MORE ON REGULATING CHARGE If you want to use gel or AGM batteries, you must have a good, reliable, user-adjustable regulator and charger. The best way to charge batteries is with a solar electric system. (Again, check first and last with “RV Solar Electric” above.) A solar system (if it has a user-adjustable regulator) will let you set the charge cut-off at
desired volts. Usually, anytime the solar system achieves that, it will cut off and drop to about 13.1 volts before resuming (some solar regs will back off to a float voltage). This gives the batteries a “rest” and keeps them from overcharging. (And, of course, at night, solar systems don’t do anything, so there’s a good rest, too.) For a backup, you can use a generator or commercial power. Make sure your generator (if it has a direct DC 12 volt charging outlet) is set to regulate at proper
volts! If it just charges through your converter, you’ll have checked that above, but recheck it with the generator running. Do the same with an independent charger. Many others are available. Deep Cycling AMP Hours and Battery Capacity Rate of Discharge: Generally 20 hours for automotive, 6 for golf cart and 8 for RV/Marine. A 180AH golf cart will, technically, give you 30 amps for its rated 6 hours, but it will not give 60 amps for three hours. (Has to do with things like heat at this higher rate due to extreme chemical action demanded–stuff you don’t want to fool with.) It will give one amp for about 105 hours, though, which is nice to know. Don’t just read AH. Read the charts when comparing batteries. Specific Gravity: Full charge SG will run from about 1.260 in an auto battery to about 1.275 in a golf cart. High SG (more acid) allows more juice (current) to be drawn–but only up to a point; then the battery deteriorates–fast. Golf cart plates are made to handle this, RV/Marine somewhat, automotive not at all. Don’t try to get more AH by adding acid (or vinegar instead of distilled water), the battery will just die sooner. Temperature: Batteries are made to perform best at 77°F. At higher temps, they put out more, but die sooner. At lower temps, they put out less, but last longer (unless you let them freeze). CABLES AND CONNECTIONS Tying the system together is important. No point spending a lot of money on batteries and chargers and wiring it up with skimpy junk. Large battery cables can be purchased from San Diego Battery Wholesale. Custom-made cable to your lengths with terminals that match your vehicle is also available. METERING BATTERIES When checking the batteries, (at rest) use these “Voltage Landmarks”. 12.6 volts = 100% MORE ON UNDERCHARGE AND OVERCHARGE CONNECTING BATTERIES IN PARALLEL, SERIES and SERIES-PARALLEL This is really simple, but it’s amazing how many RVers screw it all up! In series, volts increase; amps remain the same. In Parallel: you connect the (+) of one 12vbat to the (+) of the other. Connect (-) of one to the (-) of the other. You will then have still have a 12volt bat, but with greater amp hour capacity. This is now an ordinary 12V bat, except that instead of being in one “box,” it is in two boxes. In Series: If you were to hook two 12 volt batteries in series, you’d have 24 volts. Clearly not the thing to do unless you have a bus conversion or custom rig that uses 24Volts. However, many RVers use 6 volt (usually golf cart) batteries. E.G., Two 105AH 6v in series would still = about 105AH but @ a nominal 12V. Wiring in Series: This is now an ordinary 12V bat, except that instead of being in one “box” with cells all connected in series on the interior, it is in two boxes joined with a cable. It’s still a single 12 volt bat, electrically, so START THINKING OF IT THIS WAY and don’t confuse yourself by thinking of it as bat 1 and bat 2. At this point, you’ve got two unused bat posts — just like an ordinary 12 volt bat; one neg that goes to chassis ground and one pos that goes to normal 12V isolator/supply/etc. Series/Parallel: It’s really quite simple. The problem many people have is in thinking that this is very complicated. It’s not. The only time you think of the bats as four 6V bats is when you
disconnect them for maintenance and cleaning. And then, only to make absolutely certain that you don’t screw up when putting them back together.
TROUBLESHOOTING House Battery: The intent here is to determine if the battery itself is good, and, in its role as a “house” battery, how you can test it, the house wiring and charging circuit. Situation: You’re charging the battery from any one of several sources. Everything has been working fine; but for no apparent reason and all of a sudden, there’s no electricity. Don’t just start taking everything apart! Look around for the obvious. Is the battery still there? Is everything in one piece? (A nearby lightning strike can blow the top off.) Are the cables connected? I once spent an hour roaming around with a volt meter only to find I’d simply left the negative cable off. Steps:
Make the dumb checks first:
If there’s still no voltage, now starts the onerous process of checking the whole system.
All the above can be done with a volt meter or test lamp. In fact, a test lamp works better at continuity checks, because a volt meter might indicate power if only one strand of wire is still connected while a test lamp won’t light if it doesn’t have a circuit heavy enough for the load. TO CHECK THE BATTERY ITSELF–MORE ON RESTING VOLTAGE It can be checked with a hydrometer, but a battery can read OK and still be faulty. Here’s a good way to check a battery. It takes time, but it’s worth it:
BATTERY ISOLATORS Almost everybody has one. Most people never pay attention to them. I do. And I’ve got mine remoted to a switch on the dash to avoid the [many] problems they can cause. Most isolators send a charge to the batteries
automatically. I don’t want to do that. Normally, my solar system keeps the “house” batteries charged just fine. There are times, in bad weather, when I need to boost the batteries, so when on the road I hit the switch that goes to the charge line to house batteries and the engine alternator charges them in the normal way. A cheap, voltmeter on the dash keeps me informed when to shut charging off. How do you store a deep cycle battery when not in use?Proper Storage
While we're talking about storage, temperature is another key factor. Batteries stored in freezing temperatures or extreme heat will break down faster than other batteries. It is always best to bring your deep cycle batteries inside and store them in a cool dry place to prevent damage.
Should you leave a deep cycle battery on charge?Always keep your battery fully charged
Your Deep Cycle battery prefers to be kept fully charged when not in use, at a voltage of 12.5v or above.
How long does a deep cycle battery charge last?You should expect to get between 300 and 500 charge/discharge cycles from your deep cycle battery, but keep in mind that these numbers depend on how you use your battery and what kind of battery you have (6 volt, 12 volt, etc.)
How often should you recharge a deep cycle battery?Deep cycle batteries should be charged at least twice a year, and more often if you own a recreational vehicle. Always be sure to check the water levels in your deep cycle battery, and charge your batteries only when they are at least 30% depleted.
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