The typical car battery is designed to provide a large amount of energy for a very short time--about 5 seconds, or the time it takes to start an engine. This burst only uses a tiny amount of capacity, which is quickly replenished by the alternator. However, RVs have different types of power needs. One of the most common types of RV batteries is the "deep cycle" battery, designed to provide a small amount of energy for a lengthy amount of time. The accessories that are part of the RV experience draw power from a deep cycle battery and would quickly drain a car battery.
Deep cycle batteries for RVs and other applications are built with thicker plates and a denser active material. Glass mat and envelope separators reinforce the active material to prevent shedding and other damage. However, car batteries have active material that is highly porous, and thin plates, so that the energy can be delivered quickly for maximized power at start.
Car batteries are charged by the operation of the engine. The alternator takes the power of the engine working and converts it into replenished electrical current for the battery. If the alternator goes out, though, it will quickly drain the battery instead of replenishing it. Deep cycle batteries for RVs need to be charged periodically. Before you charge it, though, check the electrolyte level and add drinking or distilled water if needed. Use a 10 to 25 amp charger and follow the directions. Charge the battery within 24 hours of each use, so that it does not freeze; however, do not overcharge it, as that can corrode the grid and reduce the life of your battery.
