Kinds of RV Batteries

what a battery is and how it works.

Batteries used in RVs are lead acid batteries, which means they have several cells connected in series. Each cell produces approximately 2.1 volts, so a 12-volt battery with six cells in series produces an out put voltage of 12.6 volts.

Lead acid batteries are made of plates, lead and lead oxide submersed in electrolyte that is 36 percent sulfuric acid and 64 percent water. Lead acid batteries don’t make electricity they store electricity. The size of the lead plates and the amount of electrolyte determines the amount of charge a battery can store.

Different batteries in an RV.

The battery used to start and run the engine is referred to as a chassis battery or a starting battery. Vehicle starters require large starting currents for short periods. Starting batteries have a large number of thin plates to maximize the plate area exposed to the electrolyte. This is what provides the large amount of current in short bursts. Starting batteries are rated in Cold Cranking Amps (CCA). CCA is the number of amps the battery can deliver at 0 degrees F for 30 seconds and not drop below 7.2 volts. Starting batteries should not be used for deep cycle applications.

HOUSE OR COACH BATTERY:

The battery or batteries used to supply 12-volts to the RV itself are  referred to as house batteries. House batteries should be deep cycle batteries which are designed to provide a steady amount of current over a long period. Starting batteries and marine batteries should not be used in this application. True deep cycle batteries have much thicker plates and are designed to be deeply discharged and recharged repeatedly. These batteries are rated in Amp Hours (AH) and more recently Reserve Capacity (RC).

The amp hour rating is basically, how many amps the battery can deliver for how many hours before the battery is discharged. Amps times hours. In other words a battery that can deliver 5 amps for 20 hours before it is discharged would have a 100 amp hour rating 5 Amps X 20 Hours = 100Amp Hours. This same battery can deliver 20 amps for 5 hours 20 Amps X 5 Hours = 100 Amp Hours. Reserve Capacity rating (RC) is the number of minutes at 80 degrees F that the battery can deliver 25 amps until it drops below 10.5 volts. To figure the amp hour rating you can multiply the RC rating by 60 percent. RC X 60 percent

The two major construction types of deep cycle batteries are flooded lead acid and Valve Regulated Lead Acid. Flooded lead acid batteries are the most common type and come in two styles. Serviceable with removable caps so you can inspect and perform maintenance or the maintenance free type. In VRLA batteries, the electrolyte is suspended in either a gel or a fiberglass-mat. Gel cell batteries use battery acid in the form of a gel. They are leak proof and because of this, they work well for marine applications. There are several disadvantages to gel cell batteries for RV applications. Most importantly, they must be charged at a slower rate and a lower voltage than flooded cell batteries. Any overcharging can cause permanent damage to the cells. Absorbed Glass Mat, or AGM Technology, uses a fibrous mat between the plates, which is 90 percent soaked in electrolyte. They are more expensive than a standard deep cycle battery but they have some advantages. They can be charged the same as a standard lead acid battery, they don’t loose any water, they can’t leak, they are virtually maintenance free and they are almost impossible to freeze.

The life expectancy of your RV batteries depends on you. How they’re used, how well they’re maintained, how they’re discharged, how they’re re-charged, and how they are stored, all contribute to a batteries life span. A battery cycle is one complete discharge from 100 percent down to about 50 percent and then re-charged back to 100 percent. One important factor to battery life is how deep the battery is cycled each time. If the battery is discharged to 50 percent everyday, it will last twice as long as it would if it is cycled to 80 percent. Keep this in mind when you consider a battery’s amp hour rating. The amp hour rating is really cut in half because you don’t want to completely discharge the battery before recharging it. The life expectancy of a battery depends on how soon a discharged battery is recharged. The sooner it is recharged the better.

Battery Use and it’s consequences.

If most of your camping is done where you are plugged into an electrical source then your main concern is just to properly maintain your deep cycle batteries. But if you really like to boondock you’ll want the highest amp hour capacities you can fit on your RV.

Deep cycle batteries come in all different sizes. Some are designated by Group size, like group 24, 27 and 31. The larger the battery the more amp hours you get. Depending on your needs and most importantly for RVers, the amount of space you have available, there are several options when it comes to batteries.

You can use one 12-volt 24 group deep cycle battery that provides 70 to 85 AH.

You can use two 12-volt 24 group batteries wired in parallel that provides 140 to 170 AH. Parallel wiring increases amp hours but not voltage.

If you have the room, you can do what a lot of RVers do and switch from the standard 12-volt batteries to two of the larger 6-volt golf cart batteries. These pairs of 6-volt batteries need to be wired in series to produce the required 12-volts and they will provide 180 to 220 AH. Series wiring increases voltage but not amp hours.

If this still doesn’t satisfy your requirements you can build larger battery banks using four 6-volt batteries wired in series / parallel that will give you 12-volts and double your AH capacity.

The two most common causes for RV battery failure are undercharging and overcharging. Undercharging is a result of batteries being repeatedly discharged and not fully recharged between cycles. If a battery is not recharged the sulfate material that attaches to the discharged portions of the plates begins to harden into crystals. Over time, this sulfate cannot be converted back into active plate material and the battery is ruined. This also occurs when a battery remains discharged for an extended period of time. Sulfation is the number one cause of battery failure. The second leading cause of battery failure is overcharging. Overcharging batteries results in severe water loss and plate corrosion. The good news is both of these problems are avoidable.

More Electrical Stuff (for My personal knowledge)

What is a deep cycle battery?

Blobber: RVs come equipped with deep cycle batteries for the coach. Most RVs come with a single Group 24 deep cycle battery. Deep cycle batteries are rated in amp/hours. How many amps the battery can deliver for how many hours before the battery is discharged. Deep cycle batteries are designed to be discharged over and over again and still take a charge. If you enjoy dry camping (without hook-ups) you depend on your deep cycle battery(s) to take care of your 12-volt needs. You can purchase a deep cycle battery with a higher amp/hour capacity that will last longer. The higher the amp/hour capacity is the larger the battery is. If you have room for a larger battery and enjoy dry camping you may want to consider a Group 27 or Group 31 deep cycle battery.

INVERTERS: When you need a little power and don’t want to turn on the generator.

Blobber:  Inverters are nice to have at times when you are dry camping and/or when you aren’t plugged into an AC Source. Batteries produce power in Direct Current (DC) that run at low voltages. Power companies and AC generators produce sine wave Alternating Current (AC), which is used to operate 120-volt appliances and electronic equipment. An inverter takes 12-volt DC power from your RV batteries and electronically changes it to 120-volt AC.  RVers use an inverter just to watch TV or charge their personal computer. Some with more powerful batteries use an inverter to operate microwaves, coffee pots or other larger appliances. When you purchase an inverter the inverter’s output capacity must be capable of operating the loads that will be placed on it.

Two different capacity ratings of Inverters you should look for.

Continuous output rating and surge capacity rating.

Continuous output is the maximum wattage the inverter can output for a long time. Surge capacity is the maximum wattage the inverter can output during initial start up.

All appliances require more power when they are first turned on, compared to what they use to keep them running. An appliance can use as much as two or three times the amount to start then what they use to run, so the starting power required for any appliance that you plan to use with the inverter must be within the surge capacity rating.

Two types of inverters: Modified sine wave inverters and true sine wave inverters.

The Difference: A true sine wave inverter is mucho expensive, but they are capable of producing power as good as your home power company and all appliances and electronic equipment will run as they are intended to. Realize: You are drawing the power from your RV batteries and any power used has to be put back in through some type of effective charging system.

Blobber: When you’re plugged in, in someone’s driveway!

Plugged in to a 15-amp outlet, exercise caution. When the A/C compressor kicks in, it requires more amps (about 13) (and think about when you have it cycling on auto) … more power whacking the supply than it does once it is running. Because of this you need to turn all appliances off before starting the A/C, to include switching the refrigerator from A/C to LP gas.
Once it is running it may be possible to use a small appliance or electronic equipment that operates on low amperage, like a TV, You need to monitor the voltage to prevent damaging any appliances or electronic equipment.

Blobber: Long extension cord must be #12 wire or lower, (heavier gauge) to keep the amount of voltage drop from causing problems.”

Reply: If possible, no extention cord is better.

Purchase an RV extension cord that is compatible to the electrical system of your RV, and have it on hand. If you do purchase an extension cord somewhere else I recommend 10-guage wire and use as short of a cord as possible.

Bloomer: I have my RV plugged in and the refrigerator on all of the time in my driveway, will it do damage?

The RV should be on level ground so the refrigerator operates properly and you will need to monitor it for when it needs to be defrosted.

Here’s the concern: The coach battery. Whenever the RV is plugged in the coach battery is being charged. It’s really just a trickle charge, but over time it can deplete the electrolyte levels in the battery cells. You need to check, or have somebody check the battery at least monthly when the RV is plugged in during storage.

If I plug my 30 AMP into a 50 AMP at the campground!

Electrical adapters are a necessity for RVers. Eventually you will be in a situation where you have to use some type of electrical adapter to make a connection at a campground. It may be an outdated campground or isolated area that only provides 15 or 20-amp electrical service, or the only site available is a 50-amp service for your 30-amp system. There are adapters that will go from your RV type plug and size down to household type outlets and adapters that go from household type outlets to all types of campground RV connections. You must exercise caution and use common sense when you use them. If you have a 30-amp system and you have to use a 50-amp service use your RV electrical system exactly the same way you do when you’re plugged into a 30-amp service. In other words don’t try to run anymore than you normally would.

Bloomer: The coach battery in our motorhome won’t start the generator and other times it will. My question is why isn’t the RV battery charger keeping my battery charged when I leave it plugged in all the time?”

Answer: The battery charger in the RV converter provides a trickle charge and is only designed to keep the coach battery(s) topped off. It is not designed or capable of recharging a battery that is completely discharged or damaged. The automotive alternator also charges the coach battery when you are driving the RV. The alternator is probably charging the battery enough to start the generator sometimes after driving for a while, but the RV battery charger can’t charge it enough to start the generator when it’s plugged in. The constant charging from leaving it plugged in all the time can deplete the electrolyte level in the battery(s) cells. Depending on how often the battery(s) is being charged will determine how often it needs to be checked. You should check the battery(s) at least monthly and if you use the RV on a regular basis and / or you leave it plugged in when you’re not using it you may need to check the battery(s) more often.

RV ELECTRICITY

An RV actually has three separate electrical systems. It has a 12-volt DC automotive system, a 12-volt DC coach system, and a 120 volt AC coach system. Lets discuss the 12-volt DC and 120 volt AC coach systems.

Most full service campgrounds will provide you with an external 120 volt electric source. Your heavy-duty power cord which is normally about 25 feet long. It will either be a 30 Amp or 50 Amp system.

When you plug into the proper campground electrical source it will supply power throughout your RV. A 120 Volt AC power source if you are going to use the microwave, roof air conditioner, the refrigerator in the electric mode and the 120 Volt electrical outlets.

NOTE: Everything else in the camper works off of 12-volt DC power. When you are plugged in to power, a portion of the 120 volt AC current is converted to 12-volt DC current for the items in the RV that work off of 12 volts, for instance, the overhead lights, the furnace fan, and the fan over the range, the vent fan in the bathroom, the water pump, LP gas leak detector, stereo, and the refrigerator when it’s in the LP gas mode. If you look at the RV’s power distribution panel you will see circuit breakers like you have in your house for the 120-volt AC side, and automotive style blade fuses for the 12-volt DC side.

When you are not plugged into an external power source you can still use the 12-volt DC system if you have a 12-volt deep cycle marine battery on your unit. As long as the battery or batteries are charged you can use everything in the RV except the microwave, roof air conditioner, the refrigerator in the electric mode and the electrical outlets. If you have a motorhome, or you’re going to purchase a motorhome, it will have a battery for the automotive system and an auxiliary battery for the coach system. The coach battery is charged whenever the motorhome is running; the generator is running, or when it’s plugged into an external electrical source.

MAINTAIN YOUR BATTERIES !!!!

Don’t work around batteries with an any open flame. Vapors from the batteries can ignite, combust, causing serious damage. To prevent the possibility of arcing turn off any 12 Volt power sources and disconnect the negative battery cable before working on or around the batteries. If you have a maintenance free AGM or Lithium battery you will not be able to perform some of these checks. The color of the eye on the battery will indicate the condition of a maintenance free battery. Check your owner’s manual for these batteries needs.

Constant charging depletes electrolyte levels in batteries. Inspect electrolyte levels and add distilled water as required. Add water until it reaches the split-level marker in each cell. Do not overfill.

Inspect all battery cable and terminal connections. Keep all connections clean and tight. Do not over tighten. When battery terminals are clean and tight on the battery post spray the terminals with a battery terminal protector to prevent corrosion.

To clean the battery itself use a diluted baking soda and water solution. After cleaning the battery flush it thoroughly with water.

Check the state of charge and keep batteries fully charged. Specific gravity readings for a charged battery should be between 1.215 & 1.250. If you remove the batteries for storage charge them to a full charge and check them periodically during storage. Re-charge as necessary. Follow proper charging instructions for the type of battery. Deep cycle batteries require a lower amp charge over a longer period of time.

There are numerous electronic devices and equipment in your RV that can drain the coach battery when you’re not using the RV. Some examples are; the TV antenna booster, the LP gas leak detector, clocks in radios, or just leaving a 12-volt light on by accident. If your RV is not equipped with a battery disconnect switch you can purchase a battery disconnect, from an RV dealer, that can be installed directly on the battery post. When you aren’t using the RV or have no requirement for the coach battery you simply raise a lever and disconnect the battery. A battery disconnect can be installed on the chassis battery too.

THE GENERATOR:

Motorhomes also provide an additional source of 120 volt AC power with an onboard power generator. A generator offers you the convenience of 120-volt AC power whenever you need it, making the unit fully self-contained. The fuel supply for the generator comes directly from the motor home fuel tank. The system is designed so that when the fuel tank gets to 1/4 tank full the generator will stop running so it doesn’t use all of the fuel in the motor home. Some motor homes have an automatic switch over from an external power supply to the generator. Other motor homes require you to plug the motor home power cord into a generator receptacle on the motor home to use the generator.

Most Common System: a 30 Amp system is the most common on RV’s. You’ll see a large three-prong, heavy duty 30 Amp, 120-volt plug.

Most campgrounds you go to will provide you with a 30 Amp outlet that your RV power cord will plug directly into which is different than boondocking in your neighbors driveway. If you go to a friend’s house that has a regular house type outlet there are adapters that you can use to go from your RV plug to the house type outlet. NOTE: When you do this you are plugging into a 15 Amp or 20 Amp power source. This means you will be limited as to what appliances you can run in your RV.

DANGER:

It is even possible to damage some appliances if they are not getting the required amperage to operate properly. For example you plug into a 15 Amp outlet and you are using a small appliance that is drawing 5 Amps, that leaves you with 10 Amps. Now you turn the roof air conditioner on and when the air conditioner compressor engages it needs about 13 Amps, but it’s not available, and it damages the air conditioner compressor.

Even with a 30 Amp service you need to be selective about what you are using. If you try to use too much the RV will let you know by tripping a breaker in the distribution box and hopefully no harm will be done. There is a short formula that may help you with this. 30 Amps X 120 Volts = 3600 watts. This is the total amount of power you can use before you overload the system. Think of it like this, with 3600 watts you could use 36 one hundred watt light bulbs. When you turn on the 37th light you will probably trip a breaker.

Take a voltmeter along with you that you can plug right into one of the outlets. Campground electricity varies depending on the demand placed on it. On a hot night, If everybody is running his or her air conditioner the voltage may drop below an acceptable level, and it would be wise to wait until it is restored back to normal. You can glance at the voltmeter every time you walk by it and save yourself untimely and costly repairs to your RV appliances. Voltage below 105 volts or above 135 volts can damage electronic equipment and appliances.

Most appliances have a label telling you the required wattage or amperage is to run the appliance. The amperage draw for some common RV appliances and electronics.

  • Coffee maker – 8.3 amps
  • Converter – 8 amps
  • Hair dryer – 9 to 12 amps
  • Microwave – 13 amps
  • Refrigerator – 2.8 amps
  • Roof a/c 13.5 amps
  • TV – 1.5 amps
  • Toaster – 8 to 10 amps
  • VCR – 2 amps
  • Electric skillet- 6 to 12 amps

RV Electrical Systems – Good Info

Is the converter is operating any time you plug into a 120 volt AC system (30 Amp), does this mean you only have 22 amps to work with (30 minus 8 = 22.)?

What your RV converter does. When you plug your RV into an electrical source, or when you use the onboard generator, the converters job is to reduce 120 volts AC down to 12 volt DC to supply power to all of the 12 volt appliances and accessories in the RV. When you are not plugged into an electrical source your RV battery supplies the power to all of the 12 volt appliances and accessories in the RV. The converter basically prevents your RV battery from draining when you’re plugged in.

Two types of amperage draw concerning your RV. The AC amps we are using and the DC amps we are using.

When you plug your RV into an electrical source and use 120 volt appliances, eg.: the roof air conditioner, the microwave, the TV … you are drawing amps from the available supply at the campground, usually 30 or 50 depending on your RV electrical system and the electrical supply you are plugged into. When you’re plugged into an electrical source and you use DC appliances and accessories like fans, lights, pumps or the TV antenna booster you are drawing amps from the converter.

Simplified: When you plug your RV into a 30 amp electrical supply, you only use 120 volt appliances. You’re using the available amps from the 30 amp electrical supply for whatever 120 volt appliances are running, but the converter is drawing almost 0 amps because you’re not using any DC accessories. It will use a small amount for items like the LP gas leak detector, clocks or maybe an aisle light, but not enough to really affect the amperage you are plugged into.

Your RV converter is rated for a certain amperage i.e. 30 amps, 45 amps, 55 amps. In other words a 45 amp converter is capable of running 45 amps worth of 12 volt appliances in the RV. When your RV converter is working at its maximum capacity, which in this case is producing 45 amps for 12 volt appliances and accessories, it is drawing a full 8 amps out of the 30 amps available from the campground electrical supply.

If  you’re plugged in and you’re using a couple of 12 volt overhead lights (2 amps) and a ceiling fan (4 amps). In this case your converter is drawing very little from the camp grounds 30 amp electrical supply. In another scenario let’s say you’re using a lot of 12 volt overhead lights (8 amps), you’re running the furnace fan (11 amps), water pump (4 amps), TV antenna booster (8 amps) range hood fan (2.5 amps), and the battery is being charged by the converter charger (3 amps). Now, when the converter is running close to its full capacity it draws the full 8 amps from the campgrounds 30 amps, leaving you with 22 amps for other 120 volt appliances and accessories. As you can see it’s unlikely that all of this would be happening at one time. The bottom line is the converter amperage draw will fluctuate depending on the 12 volt demand placed on it.

2nd Question: I know my converter is also a battery charger so why won’t it bring my discharged batteries back to a full charge? RV converters do provide a charge to your RV house batteries, but only a small portion of the converters amperage rating is used for this. Normally 3 to 5 amps, which are not nearly enough to charge batteries that are discharged.

The converter battery charger is designed to keep the house batteries topped off with this trickle charge. Another problem with older RV converters is they charge at a fixed voltage in the range of 13.5 volts. If your batteries are fully charged this can be too much for a float charge and over time it will deplete the water level in the batteries cells. This is why it’s important to check the water level in your batteries on a regular basis, especially when you leave the RV plugged in for extended periods of time. You need a three stage charger that can provide a bulk charge then an absorption charge and finally a float charge. Newer RV converters on the market are capable of charging the batteries this way.

Here are some typical amperage draws for appliances and accessories commonly used in RV’s. This is  a basic guide to assist you in how many amps you are using at any given time. If you need to know exact amperage ratings you can check the data plate on any motors, appliances or electronic equipment you are using. This information might provide wattage requirements rather than amps. Here are a couple of simple formulas to help you convert some common electrical terms.

Wattage % Volts = Amps
Amps X Volts = Wattage

One other thing to keep in mind is many RV appliances require more amps to start the appliance than they do to run the appliance. A roof air conditioner can draw 16 amps to start, but may only use 13 amps once it is running.

120 Volt AC Amp Ratings
Appliance or Electronic Equipment Estimated Amps
Air Conditioner (X number of A/C) 12-16 Amps
Blender 5-6 Amps
Coffee Maker 5-8 Amps
Compact Disc Player 1 Amp
Computer (Laptop) 2-3 Amps
Converter 1-8 Amps
Crock Pot 1-2 Amps
Curling Iron <1 Amp
Drill 2-6 Amps
Electric Blanket 0.5-1.5 Amps
Electric Fan 1 Amp
Electric Water Heater 9-13 Amps
Electric Skillet 6-12 Amps
Hair Dryer 5-12 Amps
Iron 5-10 Amps
Light (60 watt % 120V) <1 Amp
Microwave 8-13 Amps
Microwave (Convection Oven) 13 Amps
Refrigerator in AC mode 5-8 Amps
Space Heater 8-13 Amps
Television 1.5-4 Amps
Toaster 7-10 Amps
Vacuum (handheld) 2-6 Amps
VCR 1-2 Amps
Washer/Dryer 14-16Amps
12 Volt DC Amp Ratings
Appliance or Accessory Estimated Amps
Aisle Light 1 Amp
CO Detector 1 Amp
Fluorescent Light 1-2 Amps
Furnace 10-12 Amps
LP Gas Leak Detector 1 Amp
Overhead lights (Per Bulb) 1 Amp
Porch Light 1 Amp
Power Roof Vent 1.5 Amps
Radio/Stereo 4 Amps
Range Hood (Fan & Light) 2-3 Amps
Refrigerator (LP Gas Mode) 1.5- 2 Amps
Security System 1 Amp
Television (12 volt) 4-5 Amps
TV Antenna Booster <1 Amp
TV Antenna Booster 12 Volt outlet Up to 8 Amps
Variable Speed Ceiling / Vent Fan 4 Amps
VCR Recorder / Player 2 Amps
Water Pump 4 Amp

This should clear up any confusion on the difference between using amps supplied by the campground electrical source (AC amps), and using amps supplied by the converter (DC Amps).