RV and Marine Battery Maintenance

Your RV batteries are crucial to the functionality of many systems in your RV or boat. You usually have two battery systems: a starting battery for the engine and one or more deep cycle "house batteries" to power your lights and appliances in the living area. Unless you are plugged into 120 volt shore power they are the primary source of power for lights, water pump, radios, control boards in appliances, and the fan for your furnace. If you run out of battery power, you may find the nights get pretty cold when your furnace stops working. It is ironic that when the battery voltage gets low, the furnace fan will not shut off. So it continues blowing cold air and further discharges the batteries. So, if you wake up in the middle of the night and the furnace is continually blowing cold air, turn it off to conserve what little charge is left in your batteries.  Be sure to check to make sure you didn't run out of propane, which can be another reason the furnace doesn't work.  And those wonderful home-like sinks, showers, and toilets that make life easy don't function at all if there is no power for the water pump.

An old rule of thumb says batteries should be replaced about every 3 years, but "your mileage may vary".   Newer battery technology seems to have extended the life of some batteries.  Lack of maintenance and abuse will significantly shorten battery life. Proper maintenance and usage can prolong it. If your batteries are three or more years older and are not delivering the performance  you expect, it may be time to replace them -- or at least take them down and get them tested.  Of course, the quality and original rating of the battery are also significant factors. So what constitutes abuse and what is proper maintenance? Abusing your batteries consists of not keeping them properly charged, frequently running them way down, letting the connections become loose or corroded, or letting the electrolyte levels fall below normal. Some batteries are promoted as "maintenance free". Gas-mat type batteries really are, but if they are wet-cell, lead-acid batteries, you still need to pry off the caps and check the electrolyte level occasionally. Most batteries have a fluid level indicator built into the fill opening and fluid should be maintained at that level. You need to more than just barely cover the plates and less than filling to the top of the opening. Typically there should always be about 1/2" of electrolyte above the plates.  Under filling will result in low electrolyte and shorten battery life. Low electrolyte exposes the plates and can lead to immediate sulfation which quickly destroys the battery. Over filling will result in excess boiling and off-gassing and may pop the filler caps off and spew acid when the battery is being charged. Add only distilled water to top off batteries. Ordinary tap water or even bottled water contains contaminants that will reduce power and shorten battery life so it should used sparingly and only in emergencies. I have seen battery additives that are advertised to prolong battery life and restore functionality. They may be worth trying if you have batteries that are in bad shape. It is a good idea to verify electrolyte levels as part of your routine pre-trip checklist and about once a month when your RV is in storage. It is a tedious task, but well worth it considering the inconvenience in camp and the cost of replacing dead batteries.

The starting battery for a motorhome or boat is usually located in or near the engine compartment.   House batteries could be located just about anywhere.  Sometimes they are also housed in the engine compartment but moreoften they are in a separate compartment, often under the entry step, dinette, or near the generator.  Some motorhomes have a dedicated starting battery for the generator.  When I had one like that I replaced the generator starting battery with an extra 12 volt deep cycle battery and wired it in parallel with the existing coach battery to give me more power for lights, furnace, etc. in camp and extra power for starting the generator.  Many motorhomes use the coach batteries for starting the generator.  When all the batteries are located under the hood it is a good idea to check to see what is connected to each battery bank.  I once bought a motorhome with all the batteries under the hood and was very surprised when I discovered the starter was connected to the coach batteries instead of the starting battery!  Trying to jump start the vehicle with jumper cables on the starting battery didn't really do much good.

Checking the status of your batteries. It is pretty obvious our batteries have run down when we can no longer start our vehicles or when the lights in our RVs are dim or the furnace won't run. Many RVs have a battery gauge that gives you some idea of the battery condition. These little gauges are essentially volt meters marked to give you an easy to read indication of the status of the batteries.  To really know the state of your batteries you need to test the actual voltage or measure the specific gravity of the electrolyte in the battery. A fully charged 12 volt battery should have a voltage around 13.6 volts. You may get a higher reading if the batteries have been recently charged (like driving the vehicle). That is what is known as a "surface charge". Charging voltage while the alternator is operating will be 14-15 volts. Higher charging voltages, like the 18 volts I discovered coming from a failing RV converter will cause the batteries to boil and eventually "fry" them. Anything below 11.6 volts is fully discharged. You need a battery hydrometer to measure specific gravity. This is a device that draws a little electrolyte out of the cells. Some hydrometers may be calibrated so you can read the specific gravity but most of the ones I've seen in auto parts stores contain a number of different colored balls. You determine the specific gravity by observing which balls are floating or counting the number of balls that are floating.   You can't check the specific gravity of the electrolyte in sealed batteries.  Avoid discharging your batteries below 80% or 10.5 volts. Doing so can permanently damage batteries. Maintain the proper electrolyte level. Most batteries have a built in indicator that makes the electrolyte form a dome when the right level is reached in the opening. If you don't see one, fill to about 1/4" below the bottom of the fill hole or about 1/2" to 3/4" above the plates. NEVER let the electrolyte level drop below the top of the plates as that contributes to fast sulfation of the exposed surfaces.  Use distilled water to replenish the electrolyte.  Ordinary tap water can be used in an emergency, but minerals in tap water contaminate the electrolyte, reducing performance and shortening battery life. I have read you can sometimes reclaim badly sulfated batteries by adding a water containing 10% magnesium sulfate (epsom salts).  It didn't work for me when I tried it, but the batteries I treid it on were in REALLY bad condition.

Never let your batteries stay discharged any longer than necessary. Batteries deteriorate faster when they are discharged and they are likely to freeze and crack in cold climates. Fully charged batteries are protected against freezing down to at least -75°F. Even a partially discharged battery will freeze at much warmer temperatures. A good multi-stage battery charger is the best way to keep your batteries properly charged in storage. The basic charger circuit on most standard 12-volt converters supplies only a constant modest voltage that does not adequately address all the functions required to keep a battery in good condition. Converters do well at their primary job: converting 120 volt AC to 12 volt DC to power 12 volt fixtures and appliances in your RV. Their battery-charging circuits don't usually perform as well. Sometimes the charging circuit -- or the circuit board that controls the charging circuit -- fails and delivers an incorrect voltage to the batteries. I once had a faulty converter that was delivering 18+ volts to the batteries. Before I discovered the cause of the problem I was having to add water to my coach batteries at least once a week and the batteries were quickly destroyed and had to be replaced. The high voltage was literally boiling the electrolyte away and cooking the batteries! I called the converter manufacturer and confirmed that the charging voltage was way out of spec. The technician suggested I disconnect the charging circuit in the converter and use an external automatic battery charger as a less expensive and more effective solution than upgrading or even repairing the charger in the converter. I did that for a while, then replaced then entire converter with an Intelli-charger converter with the Charge Wizard. The Charge Wizard senses the battery condition and adjusts the charging voltage accordingly. It even periodically supplies an appropriately high voltage to burn off sulfates that accumulate on the lead plates and can short out the cells. I've heard user reports that this configuration has actually reclaimed badly sulfated batteries. I have used the Intelli-charger and Charge Wizard in three different motorhomes over the last 10-12 years with excellent results. The setup is 2-3 times the cost of a standard converter but to me it was worth it. We were doing a lot of dry camping in remote areas and needed full battery capacity to make it through long weekends in the desert. Replacing the existing converter is a fairly simple task that can be done by most do-it-yourselfers. Take care to note the original wiring and make the new connections correctly. Many converters simply plug into a 120-volt outlet for their shore power and have a simple 2-wire connection to the coach wiring. If the old converter is wired directly into the 120-volt system, take care to connect the wires correctly. 120-volt systems usually have black wire for "hot" and a white one for neutral with a bare copper or green insulated wire for ground but verify the configuration before connecting your converter. Some converters have built-in 12-volt circuit boards with fuses and you will have to be careful about re-connecting each circuit to an appropriately sized fuse in the new panel. It is not a particularly difficult task, but is can be tedious and requires some attention to detail. Be sure to label the old wires as you disconnect them. If you have any concerns about doing it yourself, have it installed by a qualified electrician or RV technician. Maintaining connections to similarly labeled fuses is a good idea, but it is more important to make sure you match the fuse size for each circuit. Connecting to a lower amp fuse will result in blowing the fuse. Connecting to a higher amp fuse may allow the wiring to overheat before the fuse blows possibly damaging equipment or starting a fire. The fuse sizes have been chosen for important reasons, so pay attention. NEVER replace a fuse with a solid connector just to get things going. You may cause the wiring in the circuit to overheat and cause a fire. ALWAYS replace fuses with the same size and type of fuse. Some folks "solve" a problem on a circuit that frequently blows a fuse by putting in a higher amperage fuse. NOT a good idea! The higher amp fuse will allow more current to flow and may result in the wiring getting hot, shorting out, and causing a fire. If you frequently blow a fuse, you need to inspect the wiring and evaluate the load on that circuit to determine why it is blowing. Putting too many devices on one circuit or using high-amp devices on low-amp circuits can cause fuses to blow. Damaged wiring that is shorting out may be the cause and should be repaired or replaced. Sometimes the problem is on the ground connection for fixtures or appliances so be sure to check all ground wires too.

Battery connections. Another component that requires regular attention are the battery connections. There are problems that commonly occur and can be easily detected and corrected. One is loose connections. All connections, both at the battery terminals and at the other end of the cables should be tight and clean. A second problem is corrosion. The out-gassing that occurs during charging can deposit acid on the battery connections causing them to corrode. A good way to make sure your connections are clean and secure is to remove them and clean the battery posts and the terminals. You can sometimes do this with a simple wire brush, but it is easier and more effective to use a special battery terminal brush available at any auto parts store. These typically have a tapered wire brush for cleaning the inside of the terminals and a hollow, "female" brush on the other end for cleaning the battery posts. Observe the direction of the bristles on the brushes and turn them the same way they are already pointed so they drag rather than dig into the soft lead of the terminals and posts, which damages both the terminals and the brush. Use a commercial battery cleaner spray or ordinary baking soda and water to remove corrosion and neutralize the acid before reconnecting the terminals. If the terminals are severely corroded or cannot be tightened securely you should replace the cables or at least the terminals. I prefer replacing the cables since the terminals are usually molded into the cable. Replacement battery terminals are less expensive but since they are made of steel and lead, the bi-metal connection to the copper cables tend to speed corrosion. If you have a motorhome you will normally have two different battery banks: one for the engine and one for the coach. The engine battery is normally located in or near the engine compartment. The coach batteries are usually located in an exterior cabinet or underneath the entry step. Be sure to maintain ALL the batteries in good condition. If you have two or more batteries in any battery bank and one fails, you need to replace all the batteries at the same time. Older batteries, even if they appear to be in good condition, will drain new ones and reduce the overall performance and longevity. Because the charging resistance in a new battery is different than an old one they require different charging voltages and the demand of older batteries will have a negative affect on charging the new batteries. Be sure to install your new batteries correctly. If you are simply replacing a pair of 12-volt deep cycle RV batteries or a pair of 6-volt golf cart batteries with similar batteries, be sure to maintain the original connections. Usually, but not always, the positive lead is red and the negative lead is black. Pay attention to the leads when you disconnect the old batteries and if they do not conform to this standard, label them to avoid any problems in reconnection them to the new batteries. Multiple 12-volt batteries must be wired in parallel -- both grounds connected to the vehicle ground, both positive terminals connected to the 12-volt feed to the coach. 6-volt golf cart batteries must be wired in series: connect one ground to the vehicle ground and the positive terminal from that battery to the negative terminal of the second battery. Then connect the positive terminal of the second battery to the 12-volt feed to the coach. Connecting them in series is how they provide 12-volt power. Converting from 2 12-volt RV batteries to 2 6-volt golf cart batteries will usually give you more power, better performance, and longer battery life than two 12-volt batteries, and it is easy to do -- if you follow the directions for connecting the 6-volt batteries in series, which means you will need an extra cable to connect the two batteries together. The connector should be at least the same gauge as the battery cables.

Increasing battery capacity. If you run out of power during dry-camping trips you many need to increase your battery capacity. The simplest way to do this is to get a bigger, more powerful battery. However, most RV deep cycle batteries are already the size of Group 27 car batteries and are already maxed out. If that is the case you'll need to add batteries. If you have a Group 24 battery and have room for a Group 27, that would be an easy and fairly inexpensive upgrade. You can also add one or more additional 12-volt deep cycle batteries, wired in parallel with the exiting battery. The best time to update your battery capacity is when you have to replace a battery. You don't want to mix batteries of different types or ages in the same battery bank. They need to be matched or else they'll drain each other or cause charging problems where some batteries are over charged and some are undercharged due to the differences in internal resistance. The best way to increase battery capacity is to use 6-volt golf cart batteries, with pairs wired in series to create 12-volts. These batteries have more capacity than 12-volt deep cycle batteries and are designed to take the heavy loads and frequent deep discharging and charging necessary to operate golf carts. A pair of 6-volt golf cart batteries will take up about the same space as a pair of 12-volt deep cycle RV batteries, but will deliver much better performance. Make sure you wire them in series. That means wiring the positive terminal of one battery to the negative terminal of the other, then treating the two batteries together as if they were one big 12-volt battery. If you are upgrading from two 12-volt batteries to two 6-volt batteries, you will need an extra cable to connect the two batteries together. The original RV wiring is usually designed for the parallel connections needed when using two 12-volt batteries and would be connected with the hot to the positive terminal of one battery and the ground to the negative terminal of the other when using 6-volt batteries.

There is nothing mystical or scary about RV battery systems. A little regular and simple care will keep them in good condition and allow you to get the most out of them. But ignore them, and you will eventually reap the rewards of cold nights when the batteries get too low to run the furnace and/or the expense of replacing dead batteries before their time. If, even after good maintenance, your batteries fail to deliver sufficient power, review your charging procedures to make sure you are charging them adequately between uses. If the batteries fail to hold a charge, they will need to be replaced. If you are running a single battery to power your coach and frequently run out of power, you may have to find a place to install a second battery to meet the demands you are placing on your battery system. If there isn't room for an additional battery near the existing one, make sure the second battery is installed in a place where it is vented to the outside and connect the batteries using heavy-duty battery cable, typically "0000" gauge. You may have to go to a welding supply store to find heavy enough cable or you might find heavy duty jumper cables that will be sufficient. Smaller wiring will diminish performance and create a potential fire hazard.  12 volt DC electrical systems are safe to touch.  You won't get a shock like you do from your 120 volt household circuits but if you short out the hot wire you will get sparks or melt wires.  

Keeping your batteries charged. We usually give little thought to charging the batteries on our daily driver vehicles because driving them charges the batteries without us having to do anything special. But RVs or tow vehicles that get infrequent use need external battery charges to maintain the batteries between trips. Battery Tender is a very popular brand. You may need two separate chargers for a motorhome: one for the starting battery and a second one for the coach battery bank -- unless you buy a multi-bank charger.  I use a generic battery tender on my starting battery and take advantage of the superior charging capabilities of my Intelli-charger converter with Charge Wizard to maintain my coach battery bank. There are chargers designed to handle multiple battery banks but it is probably less expensive to just put separate chargers on each bank. I like to install my chargers so they are active whenever there is 120-volt power available in the coach -- from shore power or from the on board generator. That way I don't have to think about plugging in the charger in camp or before I store my coach between trips.  Be aware of adding chargers if there is already a charger built into the converter.  Using multiple chargers at the same time may conflict with each other and produce unpredictable and undesireable results.

Solar battery charging is a an easy and free way to keep your batteries topped off -- once you buy the solar panels and charging system.  Small chargers that will help keep fully charged batteries fully charged in storage where they're not getting heavy use are not terribly expensive.  I've see them under $20.  They are about the size of the top of a carton of eggs and about 1/2" thick.  They plug in to the cigarette lighter in your vehicle and are normally placed on the dashboard.  They are not powerful enough to recharge depleted batteries or power equipment or lights.  Large solar panels can be mounted on the roof of your RV and with enough panels and controllers can charge depleted batteries and run some 12-volt lights and appliances.  But solar systems of these size are not cheap.  Expect to pay in the neighborhood of $300 for a start up configuration.  Large solar arrays can be very helpful when boondocking and using inverter power.  And the electricity is free -- once you've re-couped the setup cost -- saving you fuel cost for running  your generator.  Solar power is especially useful on boats if you don't have 120 volt power at the dock to recharge your batteries.

You can charge batteries using your on board generator, but most experts say it is faster and more efficient to use the vehicle alternator.  Some portable generators have a 12-volt battery charging circuit built in.  I have a small, 850 watt generator that does.  It generally isn't powerful enough to run mainline 120-volt appliances but it is a pretty good alternative for emergency battery charging when boondocking.  If you can get your hands on an old Army hand-crank generator, or bicycle pedal generator, they could be used to charge batteries too.   They used to be available in Army Surplus stores, but these days they may be hard to come by.  I did find a pedal generator on Amazon.com for about $200.  You might build your own using an automobile alternator.  Use one with a built-in voltage regulator and you should be able to wire it directly to your batteries for charging.  Then you just need to rig up a crank and pulley to drive the alternator.  I've also seen plans for building your own wind powered generators using an automobile alternator, but designing and building the blades is probably beyond the time and effort most of us are willing and able to invest in such a project. Plus transporting the blades and tower and setup in camp is cumbersome and wind is unpredictable.

Proper battery maintenance will ensure you get best possible performance and longevity from your RV batteries.

Charge!