Battery Facts and Maintenance

Take a quick look around your RV and try to find something that doesn't operate by electricity. Today's RV normally has more than one hundred pounds of wire involved with both 12 Volt direct current (DC) and 120 Volt alternating current (AC) systems. The uses of battery power have grown by leaps and bounds over the years, while basic battery technology has changed very little.

Life is hard for RV batteries, with life spans being shortened by extreme usage and lack of maintenance. Battery life ranges from six months to four years, but only 30% of deep cycle batteries the most common type used in RVs-ever reach the four-year mark. With some of the larger batteries costing more than $200, upkeep can be expensive, making proper maintenance critical.

Batteries act as power storage devices. Electrical power is placed into the batteries by creating a flow of electrons that can be accepted by the battery. This charge-or flow of electrons-can be created by a generator, alternator, power converter, battery charger, or even another battery.

After the battery is charged, power can be withdrawn. Generally this takes place through electrical devices designed to accept the stored power. But in the case of accidents, short circuits, or wiring faults, this can happen inadvertently, with undesired results. When power is unintentionally drawn from batteries, fires, explosions, acid damage, and burns can occur.

If a 12v battery is fully charged, with its six cells producing 2.1v each, it should be capable of producing 12.6v. The charging system's job is to reach this maximum point of charge and maintain it so the battery can serve its purpose of supplying power.

The battery's discharge cycle begins when a draw is placed on the power stored in the battery. This process causes a chemical change to the surface of the plates that coat the positive and negative plates with lead sulfate. The chemical change, called sulfation, is the normal result of electron transfer within the battery. The more plate surface that becomes coated with lead sulfate, the less power the battery will be able to store because of the loss of surface area for the electrolyte to work on.

There are various case styles for batteries, but the internal workings of most lead/acid batteries are similar. The negative plate is constructed of sponge lead, while the positive plate is made up of lead oxide paste. Both are held in a bath solution of 30% sulfuric acid and 70% distilled water. The solution, called electrolyte, causes a chemical reaction that produces power.

There are several types of batteries, but lead/acid or wet cell type is the most common type used in the automotive industry. The current wet-cell lead/acid battery has been in use for more than 100 years.

When working around batteries, remove all jewelry, including metal watchbands. Anything that conducts electricity can be dangerous around batteries. Polyester clothing has a natural resistance to battery acid, so it's a good choice when working around batteries. Always wear safety goggles to protect your eyes.

When you perform your monthly ritual of topping off the battery water, it's a good time to also test your batteries. A simple device called a hydrometer is used to test the electrochemical charge of lead/acid batteries. A hydrometer, which looks somewhat like a turkey baster with a floating scale in it, measures the amount of sulfuric acid in the electrolyte bath. A low reading indicates the acid has been absorbed into the lead plates, leaving the battery with a low level of charge. Charging the battery drives the acid out of the plates and back into the electrolyte bath solution.

Follow these simple steps to test your battery with a hydrometer:

1. Do not add water to any of the cells even if they seem empty.
2. Fill and drain the hydrometer two to three times before drawing a sample for reading.
3. Fill the hydrometer with electrolyte. Have enough sample fluid of electrolytes in the hydrometer to completely support the float.
4. Check all the cells in the battery, repeating the steps above.
5. Replace vent caps and wipe of any electrolyte that may have spilled
6. Correct the reading standard of 80° by adding .004 for every 10° over 80° and subtracting .004° for every 10° below 80°.
7. Use the following table to determine the state of charge in each battery cell. It shows open circuit voltage test values done with a hydrometer.

When several batteries together serve as a power source, one battery in the set can be a charging source for another battery with less charge. This can mask the need to replace the battery that's low on power. Assume, for example, there are four 8-D batteries in the RV's battery system, and the batteries have been providing good service for several years. If you begin to experience problems and have a battery dealer do a diagnosis, you may find that there are some dead cells in one of the batteries. It may seem okay to replace the single problematic battery, but because batteries can draw power from each other, that wouldn't be the best solution.

First, sulfation of the plates on the three remaining batteries may cause them to produce fewer than their maximum 2.1v each. If the plates are partly covered with lead sulfates, chances are, they're producing less than they should be.

In addition, a new battery's tendency is to charge any older, weaker batteries in the system. Instead of the new battery providing power to the RV electrical system, it attempts to charge older batteries to its own level, resulting in gross power loss. Replacing only one of the batteries prevents you from maximizing your batteries' potential and may be damaging to the new battery.

All batteries are marked with the date of manufacture. To help prevent damage to any one of your batteries, always try to get batteries built within three months each other. Never mix batteries into a battery bank with more than a six-month difference between manufacturing dates.

Recharging your batteries is simple and safe if some basic safety tips are observed. Batteries should only be charged in well-ventilated areas. Do not charge in areas where sparks or flames are allowed or where temperatures rise above 120°. Never attempt to charge a frozen battery. Always verify the charger voltage settings are correct for both the voltage level and the battery type.

Prior to charging the battery, make sure there's enough water to cover the plates. Use only distilled or de-ionized water. Never use water with a high mineral content. Open the vent caps and check the electrolyte level; the minimum level is to the top of the plates. If the water is below the top of the plates, add just enough water to cover the plates. Do not add water to the point that the water level reaches the cap. If the battery has been discharged enough to leave the plates exposed and it will not take a charge, take it to a battery specialist for further evaluation. After the batteries are charged, check that the water level is about one-eighth of an inch below the bottom of the fill well before replacing the vent caps tightly. Check your water level again after you've fully charged the battery and add more if necessary.

When charging, don't expose the plates to air or add acid directly to a battery. Before you add the batteries to your RV's battery bank, charge them according to the manufacture's instructions. After, proper charging is complete, install the battery into the battery bank, making sure that all connections are clean and corrosion free.

Lead/acid flooded cell batteries may have their life extended by the process of equalizing. This is a deliberate overcharge of batteries after they have received their normal charging. An equalizing charge uses a higher voltage with very low amperage to help eliminate the stratification and sulfation conditions that lower battery performance. If your batteries are the flooded cell type, you can equalize them by following these steps:

1. Remove all loads from the batteries.
2. Connect the battery charger or your inverter if it has an equalizing stage in it.
3. Set the charger for the equalizing voltage.
4. Turn on the charger and start charging batteries. The batteries should begin bubbling vigorously.
5. Take specific gravity readings every hour unless your charger is an automatic type. Equalization is complete when the specific gravity values no longer rise during the gassing stage. Even though the basic lead-acid battery design is more 100 years old, the fact that it is still in use today proves that it works well. RVs use an enormous amount of power, with the batteries being the weakest link. Proper care of them will not only save money and provide longevity of the individual batteries; it will also ensure that in an emergency your power.

Electrical Term	Definition	Pressurized Water System Analogical Terms
Volt	Electrical pressure	Pounds per square inch
Amp (Ampere Current)	Quantity of flow per unit of time	Gallons per minute
Resistance (Ohms)	Restriction to flow	Pipe size, nozzle, or valve
Conductor	Wire	Pipe, tubing
Semi-conductor	Allows current flow in only one direction	Check valve
Alternator, generator, charger	Creates electrical pressure	Pump with a maximum pressure and capacity rating
Voltage Regulator	Voltage input controller	Pressure regulator
Battery	Storage tank	Pressure tank accumulator
Ampere-Hour (AH)	Amount of amps flowing times the number of hours used	Gallons per minute over a given amount of time