From the Community:

A Fundamental Guide To RV Batteries

If you want to keep the batteries in your RV working as long as possible, it helps to understand those batteries' basics. So, we asked for some guidance from Power Genix Systems and they happily provided us with some help to create this piece below.

RVs operate on lead-acid batteries. These are made up of plates made of lead or lead oxide. The plates are submerged in an electrolyte solution that mixes sulfuric acid with water in a 36 to 64 ratio. Batteries don't create electricity; they can only store it. The amount of charge a lead-acid battery can hold is set by the size of the lead plates and the amount of electrolyte it contains.

Each of the lead-acid batteries found on your typical RV contains multiple cells connected up in series. An individual cell is capable of producing 2.1 volts. A 12-volt battery will have six cells connected in series. Thus, its actual output voltage is 12.6 volts.

RVs use multiple batteries, and each battery needs to be picked to suit the job it's called on to do. The battery responsible for starting the engine, for instance, is called the starting battery or chassis batter. Its job demands large currents delivered in short time spans. This need is met by the way the battery is designed. A starting battery has lots of very thin plates in order to increase the surface area in contact with the electrolyte. The result is a larger burst of current over a shorter period.

Chassis battery performance is rated in Cold Cranking Amps or CCA. This figure describes the battery's output in amps when it is discharged for 30 seconds at 0 degrees Fahrenheit. (Voltage cannot drop below 7.2 volts in the measuring period.) Because their design is slanted towards fast, powerful discharge, starting batteries are unsuitable for deep cycle use.

The fixtures in the RV itself are powered by one or more 12-volt batteries referred to as house batteries. These are deep cycle designs intended to deliver consistent current over long periods. Neither chassis batteries nor marine batteries are suitable for use as house batteries. Inside the cells, deep cycle batteries feature much thicker plates. This enables them to discharge fully and then recharge, over and over again. House batteries are rated in Amp Hours (AH). Recently, house batteries have also been rated in Reserve Capacity (RC).

The Amp Hour rating defines how long the battery will deliver power at a given amperage. It is equivalent to amps times hours, and the two figures can be split up however you like. For example, a 100 AH house battery will deliver 5 amps for a period of 20 hours before it is discharged. The same battery, if it's delivering 20 amps, will be discharged in 5 hours. Note how in each situation, amps times hours delivers the same result: 100 AH.

The newer Reserve Capacity rating illustrates a deep cycle battery's performance in more specific terms. It is how many minutes the battery can deliver 25 amps until it reaches a discharge condition - delivering less than 10.5 volts. (RC rating assumes a temperature of 80 degrees Fahrenheit.) You can easily convert RC into AH; simply multiply RC by 60 percent (0.6).

Most deep cycle batteries in use today rely on one of two design standards: flooded lead acid and valve regulated lead acid. Flooded lead-acid batteries are still the most common type on the market. Flooded batteries come in two sub-styles: maintenance free or serviceable. Serviceable batteries include removable caps so that they can be opened, inspected, and maintained.

In a valve regulated lead acid (VRLA) battery, the electrolyte solution is bound up in a gel or a mat made of fiberglass. Gel cell batteries are preferred for several applications, like marine use. Their chief advantage is being completely resistant to leaks. These benefits are outweighed by some drawbacks in an RV context, though. Gel batteries require slower charging cycles at voltages lower than those used for flooded cell batteries. Gel cell batteries can also be permanently damaged if overcharged.

The design which incorporates fiberglass mats is called an Absorbed Glass Mat (AGM) technology. Here, fiberglass mats are placed between the battery's plates. Each mat is soaked in a 90 percent electrolyte solution. AGM batteries cost more than conventional batteries but they deliver a few key advantages. They have no special charging requirements, they don't leak, they require almost no maintenance, and they are not vulnerable to freezing.

You play the biggest role in determining how long your RV batteries last. The way they're used, the maintenance they receive, how you charge and discharge them, and how you store them - all of these factors impact the lifespan of your batteries.

A battery cycle is a circuit a battery takes from being fully charged, discharged in use, and then charged up again. Battery life will depend on how fully the battery is discharged in each cycle. A battery that is only discharged to half capacity (50 percent) in each cycle will last longer than one that is regularly discharged to 80 percent.

In effect, this means you should take a battery's amp hour rating and cut it in half if you want to maximize its useful lifespan. Letting the battery discharge fully will wear it out faster.

Battery lifespan also depends on how long you let the battery remain discharged. The sooner it is recharged, the longer it will last.

These battery basics need to be balanced against the way you use your RV. If your RV is almost always plugged in and reliant on an external power source, you simply need to ensure that your regular deep cycle batteries receive adequate maintenance. If you know you'll do a lot of "dry" camping, though, you need to outfit your RV with batteries that deliver the highest possible AH rating.

Deep cycle batteries are sold in many different sizes. They are commonly classified according to group size. Group 24, 27, and 31 batteries are all common in RV applications. It's a general rule of thumb that for more amp hours, you need bigger batteries. You have many different choices based on the amount of space you have available.

A single 12-volt 24 group battery will deliver 70 to 85 AH. Wiring two such batteries in parallel will keep the same voltage and double your AH to 140-170.

Many RVers opt to use larger 6-volt golf cart batteries. Because you need to double the voltage to suit your RVs 12-volt system, golf cart batteries need to be paired and wired up in series. A pair of 6-volt batteries typically delivers 180 to 220 AH.

To store even greater amounts of current, you can build bigger battery banks by wiring in both series and parallel. Four golf cart batteries wired up properly will deliver 12 volts and 360 to 440 AH.

RV battery failure is most often caused by either under or over-charging. Undercharging happens when batteries don't get a complete recharge between discharge cycles. Incomplete recharging causes sulfates to crystallize on the discharged parts of the plates. These sulfates permanently reduce the charge capacity of the plates and can ruin the battery over time. The same sulfation can occur if batteries remain in a discharged state for too long.

If batteries are overcharged, the plates begin to corrode and the electrolyte mixture loses water. Fortunately, both of these problems can be avoided with responsible, informed usage.

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