The RV battery is one of three energy storage methods normally found in a modern RV. The other two are propane used primarily for heating and the gasoline or diesel used for transport. When you stop to think about it, there aren't many other options for energy storage and those aren't convenient to carry around with you. Coal has been used in ships and locomotives and the U.S. has a lot of it. Hydroelectric - using the potential energy of water at elevation is convenient, but not mobile. Mass for direct energy generation (nuclear) is also not well suited for the very small needs of the typical RV. Note that the issue is storage of energy and not its generation or transmission.
Electricity is a very convenient means to move energy around. It also easily converted in light, heat, air movement, liquid movement, and other forms that help us keep comfortable. The problem is that of having a ready supply on hand when we need it. A battery is like having a reservoir of water up on a hill. We can get a little bit or a lot - that is until the reservoir runs dry. The alternative is to generate the electricity when you need it but converting hydrocarbon fuels to electricity is noisy and you can't depend upon the sun or the wind to provide just what you need just when you need it. So a battery is needed as a convenient reservoir of electricity.
A battery is a chemical reaction waiting to happen. The chemical reaction depends upon moving electrons around. Moving electrons is electrical current. How much energy is stored in a battery depends upon which chemicals are trying to react and how much of these chemicals are available to react. Battery technology is nearly 100 years old and there have not been any significant changes or improvements in that time. It is a mature technology.
Piles of reactive chemicals can be hazardous requiring careful handling and storage.
Most chemical reactions have only a volt or two of push requiring many cells in series.
It takes a lot of stuff to store a little bit of energy
Flashlight batteries: usually alkaline or perhaps zinc based and wrapped in a sealed cylinder. These are single use disposable batteries. They should not be stored in devices even though they often have long shelf lives.. Watch for leakage and any indication that the case is bulging. Properly dispose of dead, leaking, or bulging batteries
Electronic gadget batteries: usually Nickel Cadmium or Lithium based. These are rechargeable. These tend to discharge over time so should be kept charged and used frequently.
Wet cell lead acid batteries are the standard automotive type with sulfuric acid sloshing around between lead plates.
Gel Cel: a lead acid battery with the sulfuric acid in a gelled state and specially constructed so it can be sealed
Absorbent Glass Mat (AGM) batteries are lead acid batteries with the acid trapped in a fiber glass matting. They are also sealed and may be used in any position.
Lead acid batteries are the most common storage batteries because lead and sulfuric acid are readily available (natural) chemicals and can be made into inexpensive batteries with high capacities. Since both lead and sulfuric acid can be rather dangerous and caustic, these batteries require cautions in use.
The lead acid battery uses the fact that lead will react with sulfuric acid to form lead sulfate giving off two electrons and lead oxide will also react with sulfuric acid to produce lead sulfate if prodded a bit with a few electrons. So a lead acid battery is a lead anode providing electrons and a lead oxide cathode receiving electrons with sulfuric acid in between being converted to lead sulfate and water. When the battery is fully charged there is a lot of sulfuric acid and no lead sulfate. When discharged, the plates (anode and cathode) are covered with lead sulfate and in between is mostly water.
A drop in capacity of about 25% is about what you can expect from lowering the temperature 30o F or doubling the current drain. Excess heat destroys batteries while cooler temperatures decrease capacity. http://www.lightheat.com/batteries.htm provides the rule of thumb . that for every 15oF above 77oF, capacity is increased by 10% and for every 15oF below 77oF, capacity is reduced by 10%.. As temperature increases, voltage decreases and the specific gravity of a cell will also decrease. Conversely, as temperature decreases, voltage and specific gravity increase.
Temperature is a result not only of ambient air but also the current running through the battery. This is why charging, especially fast charging, needs to consider the temperature of the battery cells being charged.
Also see: Battery Myths -|- Battery Configurations
Sierra Nevada Airstreams -> Travel Trailers Owner's Guide -> Understanding