The 12volt Side of Life ( Part 1) .
Welcome to the page of all things 12 Volt! The information here was either excerpted from various sources on the web and in the public domain, or results directly from my personal experience. When researching battery specs for this page, I was amazed at the wide variance in some of the information. For instance; the charts that show voltage related to state of charge. almost every chart I looked at had different voltage values. I had to make a judgment call and pick the chart that best matched my own observations on my own 12 volt system. I tried to keep "opinion" to a minimum in the interest of putting out good, useful information, but where the sources of the information differ, I had to make an opinion call. Just so you know. the data on batteries contained herein is the best I can come up with, but may not be gospel. Some of the suggested RV modifications require you to be at least a little handy. Don't undertake any project beyond your capabilities and be especially careful anytime you are working in proximity to the batteries. They can be really dangerous if treated wrong. acid is caustic and batteries can explode if a spark or open flame ignites the hydrogen gas they produce. Shorting the output terminals of a battery can create huge sparks and sprays of molten metal (can you say "welding"?) When working with batteries, you need to have plenty of ventilation, remove jewelry, wear protective clothing and eye wear (safety glasses), and exercise caution. Whenever possible, please follow the manufacturer's instructions for testing, jumping, installing and charging. Use proper care at all times and don't EVEN try to sue me if you screw up. I warned you! Please see the disclaimer before proceeding!
One of the best things about an RV is the self-contained power system that allows us to have all the comforts without being plugged into an electric outlet. This 12 volt system can be a joy or a headache, depending on how you maintain and utilize it. If you ignore basic maintenance, it'll let you down at the worst possible time! An understanding of the components and principles involved is necessary to get the most out of your 12 volt system. Relax, tho. it's not "rocket science". your 12 volt system is simple and very easy to understand and maintain. Let's just take a look at a block diagram of a typical RV 12 volt system.
See. there's really nothing to it! In the simplest terms, you have lights and other equipment such as water pump, fans, stereo, etc. that run on 12 volts, a battery that supplies the 12 volt power and some sort of charger to replenish the energy that you use from the battery. Of course, it's possible to add lots of useful components to this simple system to make it more flexible, but the basic 12 volt system in any RV starts with the components shown above.
As you read through this information, we will talk about all the different parts of this system and discuss some of the very useful additions and improvements that you can make yourself. Also included will be some highly technical info that you can bypass if it doesn't interest you. So, let's get started by talking about batteries. The battery is the heart of the 12 volt system. No other single component is as critical to the system's functioning as your battery system! That's why a lot of time needs to be spent talking about the care and feeding of your battery(s).
Sure, we all know what a battery is. it's that thing that goes dead when you leave the headlights on overnight! Actually, there's a little more to it than that, so perhaps a review of battery basics is in order here.
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. Batteries are not 100% efficient - some energy is lost as heat and chemical reactions when charging and discharging. If you use 1000 watts from a battery, it might take 1200 watts or more to fully recharge it. Slower charging and discharging rates are more efficient. Practically all batteries used in RV applications are Lead-Acid type batteries. Even after over a century of use, they still offer the best price to power ratio.
Batteries are divided in two ways, by application (what they are used for) and construction (how they are built). The major applications are automotive. marine. and deep-cycle. Deep-cycle includes solar electric (PV), backup power, and RV and boat "house" batteries. The major construction types are flooded (wet), gelled. and AGM (absorbed glass mat). AGM batteries are also sometimes called "starved electrolyte", because the fiberglass mat is only 90% saturated with Sulfuric acid. Flooded may be standard, with removable caps, or the so-called "maintenance free" (without caps). All gelled are sealed and a few are "valve regulated", which means that a small valve keeps a slight positive pressure in each cell. Most AGM batteries are sealed and valve regulated. Sealed gell and AGM batteries offer the convenience of no maintenance and produce less gas, so at first glance, they may
appear more attractive than standard flooded cell batteries. There is a down side here, tho. These batteries, especially the gell cell type, require precise control of the charging process to prevent permanent damage by overcharging. They also tend to be significantly more expensive and have a somewhat shorter lifespan. It all depends on what premium you put on the maintenance free aspect of it. In my opinion, the standard flooded cell battery offers better overall performance for the price and will probably last a lot longer in most common RV applications. The need to add water periodically is a small price to pay for the advantages you get. I strongly suggest that you avoid the "maintenance free" flooded cell batteries. they truly aren't a good design: they are simply a standard flooded cell battery with sealed cells. Each cell has a small valve to release excessive pressure. They still can be run low on electrolyte with heavy usage and fast charging, and there's no way to add water, so the batteries often die young.
It's important to understand the differences in battery types.
Starting batteries are normally 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 damaged and will fall to the bottom of the cells. Automotive batteries will generally fail after 30 or more deep cycles.
Deep cycle batteries are designed to be discharged down as much as 80% repeatedly, 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. Unfortunately, it is often impossible to tell what kind of battery you are really buying in some of the discount stores or places that specialize in automotive batteries.
Many Marine batteries are actually "hybrid", and fall between the starting and deep-cycle batteries, while 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. "Hybrid" types should not be discharged more than 50%.
A battery's capacity for storing energy is rated in several different ways, depending on the battery type. Starting batteries are often rated in Cold Cranking Amps or CCA. CCA is the discharge load in amps which a battery can sustain for 30 seconds at 0 degrees F. and not fall below 1.2 volts per cell (7.2V on 12V battery). This battery rating measures a burst of energy that a car needs to start on a cold morning.
Deep cycle batteries are often rated in Amp/Hours. Amp/Hour rating of battery capacity is calculated by multiplying the current (in amperes) by time (in hours) the current is drawn. For example: A battery which can deliver 4 amperes for 20 hours before being discharged would have a 80 amp-hour battery rating (4 X 20= 80).
You may also see batteries rated with a Reserve Capacity. RC is the number of minutes a new, fully charged battery at 80 degrees F. will sustain a discharge load of 25 amps to a cut-off voltage of 1.75 volts per cell (10.5V on 12V battery). This battery rating measures more of a continuous load on the battery. For RV use, this rating is a little less useful, as the common loads that RV use puts on a battery are a lot less than that 25 amp load used to determine RC.
I feel that the best bet is to consider batteries by their amp/hour rating, so that is the rating method used throughout this article.
Now that we know a little more about batteries, it becomes obvious what we should be using in the RV. Deep cycle batteries! When you unplug from the A/C line and go boondocking for a weekend, you are using only your batteries to provide power for your rig. It's not uncommon for those batteries to be fairly well discharged before you get back to civilization and plug in. Starting batteries and "Marine" batteries just aren't designed for this kind of use and will die an early death in your RV. Use only deep cycle batteries! This is so simple that you'd think it would be a no-brainer, but a lot of RVs (especially used ones!) leave the dealer's lot with starting or Marine type batteries installed. If you recently bought your rig, it may be worthwhile to check and see just what batteries you actually have installed.
Selecting the correct batteries is all about lifespan. The right batteries will last a lot longer, leaving you with more money for the finer things in life! The lifespan of a battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors. We'll talk more about maximizing the lifespan of your batteries later, but for now, here are some typical expectations for batteries used in deep cycle service:
Starting: 3-12 months
Marine: 1-6 years
Golf cart: 2-8 years
Deep cycle (L-16 type etc.): 4-8 years