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RV Battery Charging and Care FAQ's

Deep Cycle Batteries: 80% discharge and then recharging is one cycle. This would be around 11.8 voltes. 40% discharge and recharge is 1/2 cycle; and 20% discharge and recharge is 1/4 cycle. This type has fewer and thicker plates, versus "Starting Batteries", which have more, thinner plates for short bursts of high amperage. Starting batteries are NOT suitable for "house" batteries.

Most RVs come equipped not with a true deep cycle battery, but rather "RV Marine" type batteries -- a sort of hybrid between a true deep cycle and a starting battery (and less expensive for RV manufacturers to use.. These are definitely better house batteries than a starting battery would be -- so use them until they wear out and then replace them with a true deep cycle type.

Battery Types: Flooded lead acid batteries are either lead calcium "maintenance free" types, or lead antimony -- the more traditional type that has caps and to which you need to add water periodically. Most deep cycle batteries are lead antimony, since the "maintenance free" types (lead calcium) are sealed, but have low tolerance for "deep" discharge (below 40-50%). Lead antimony has higher tolerance for deep discharge, but they self-discharge faster. On balance, lead antimony is better suited for RVs, and true deep cycle batteries are of this type.

Gel Cell: Good for boats, where you're in rough seas, since the electrolyte won't leak out as it would with flooded batteries. But some problems, and in terms of utility are now totally replaced by AGM. If you charge gel cels at too high a charge, you'll actually lose some of the elctrolyte through gassing, and dry out the battery (shorter life).

AGM (absorbed glass mat) is a flooded lead acid battery, but instead of gel, it uses a fiberous mat which is 90% soaked in electrolyte. It is sealed, and the electrolyte is so immobilized that it can never come out.

Solar is nothing but a battery charger. Inverter is nothing without a battery. So need to understand batteries before you can understand either solar or inverter.

Only true way to know state of charge of a battery is to check its specific gravity. But very few RVers do this. Another fairly complicated way is to buy a meter for several hundred dollars (e.g., Link 10) that will measure that for you. The other way is to go by battery voltage. Preferred method is digital display, versus analog (needle). The idiot lights (red, amber & green) that come with most new rigs actually mean very little. The key to voltage checks is getting the battery "at rest". Yet that's virtually impossible unless you completely disconnect the battery, since there are always phantom loads (sensors, etc.). If you're plugged in to shore power, or use solar panels, they "charge" and make it impossible to know true voltage. Best time is first thing in the morning when you've not been plugged in (and before any solar influence). 12.65V is "full"; 12.47V is 75%; 12.24V is 50% 12.06V is 25%; 11.89V is just about zero.

How to know battery voltage: Only way to know for sure is to test the specific gravity of each cell. But his is so cumbersone that most RVers want another option. The built in systems of LEDs are at best an approximation. Best time to catch battery in the needed "at rest" condition is in the early morning -- unless you have solar, in which case you need to check before first light.

Primary causes of battery failure: Overcharging is one primary culprit. To charge, you need a source 14.1V ro 14.4V or more at room temperature. That's the gassing threshold for most lead acid batteries. You don't want to have higher voltage causing it to boil or "gas" from excess amperage. Gassing will occur at lower charging rates if the outside ambient temperature is hot -- such as parking on ashphalt during hot weather. Overcharging causes plate corrosion and/or water loss. In colder weather you may need to go above 14.1-14.4 volts to cause the needed gassing to stir the electrolyte. This is called reaching the edge of the gassing threshhold, which is needed to fully recharge the battery. Thus batteries will have longer life if there is a system for changing the charge rate depending on termperature. Lack of temperature compensation on inverter, charger, and solar is very important for RVs. Hot batteries require a lower voltage charge, while cold weather requires using higher voltage to "compensate" for the ambient temperatures. Unless the charging system can adjust the charging voltage either undercharging or overcharging is likely to occur. Temperature compensation is a crucial for RVs. If you don't have temperature compensation and the weather is hot, you'll have to add water more frequently, and keep batteries clean from the effects of gassing and spillage.

Undercharging is another problem, as it results in plate sulfation and electrolyte stratification. You'll know this when your battery used to last for 3 days, but now only lasts a day.

Vibration in an RV can cause some of the lead on the plate to fall off and piles up on the bottom of the battery. Eventually it builds up and will short out on the adjacent plate. by Greg Holder, AM Solar, Inc.

It is always a good idea to have jumper cables just in case your battery decides to die on you at always the most convenient times. It is also most important to know how to properly use the jumper cables so you don't accidentally fry your car's electrical system so always consult with and carefully follow the instructions provided. If you suspect that a battery is frozen, do not charge it, as it may explode! One visual sign that a battery has frozen is that the sides are bowed out. This condition is not repairable, and ithe battery will need to be replaced by a professional as soon as possible. If you need to charge your battery yourself, switch the charger to a low-charge setting. Most chargers have this feature but if not, have a professional charge the battery. Don't charge a dead battery with a car's alternator. An alternator is not designed to function as a charger, and it may be damaged or have a shortened life as a result.