RV Battery Basics

RV Trailer Battery Guide

November 1, 2011
Filed under Towing Tips, Trailer How To

Battery performance and overall condition is something that is more important to RVers than most other road warriors, and for good reason. In the grind of the daily commute, poor battery performance is usually no more than a pain in your backside – get a jump-start, call a towing service or simply get the battery replaced at the corner auto-parts store. But in the backcountry, where help isn’t always a phone call away, a dying battery can mean anything from a minor inconvenience to dire circumstances, depending on the situation.

Knowing how to check or test your batteries, how to maintain them and making the right choice when it comes time for replacement are critical components in ensuring trouble-free performance on the road. But the batteries in your tow vehicle and those used in your RV are different animals, and as such, have different requirements.

Batteries for the Tow Vehicle

Like most of the components on your vehicle, the OEM battery is a compromise to some degree. It is designed to endure the rigors of day-to-day use by average people in a variety of different climates. According to Gale Kimbrough, technical services manager for Interstate batteries, a battery’s efficiency is rated at an ambient temperature of 80? F. By and large, a hot climate such as Las Vegas, Nevada, or Phoenix, Arizona, is hardest on a starting battery, but extreme cold can shorten life as well. On average, you can expect your starting battery to deliver reliable performance for 3-5 years under normal usage. Typical signs of a dying battery are quick discharge (the battery seems to lose life after playing the stereo or running the lights for only a short time with the engine off) and sluggish starting. If, on the other hand, you notice that your lights dim with the engine running, you likely have an alternator that’s going bad, or some other problem with your charging system. Bear in mind that, if your alternator has indeed been the culprit, the constant drain on your battery may have damaged it as well.

RV battery testing can diagnose many problems.

RV battery testing can diagnose many problems.

There are two ways to have your starting battery performance tested: Conductivity and load testing. Conductivity testing is becoming more popular, because it can be performed with the battery in the vehicle, cables attached, in about a minute. Load testing can be performed by bringing a battery into most any auto-parts store, or in the vehicle with the cables disconnected. Either way, testing will tell you whether the battery is in bad (requires immediate replacement), marginal (may fail to start the vehicle in moderate to extreme hot/cold temperatures) or good (check again in about six months) condition.

When considering a new battery, most of us are prone to the “bigger is better” line of thinking. In the world of batteries, “bigger” can mean different things, and “better” in one application can be a bad choice in another. For example, most of us gravitate toward the battery with the highest possible Cold Cranking Amps (CCA) or the battery’s ability to start an engine in cold temperatures. Those of us who live in hot climates also gravitate toward high CCA batteries, because we know that hot engines can also be difficult to crank; but in this case, higher CCA is not the solution.

The higher the CCA rating, the more plates per cell the battery has, which displaces the liquid electrolyte and actually makes the battery run hotter. A hot battery doesn’t perform as intended, and as mentioned earlier, won’t last as long. A local battery shop may have a recommendation, if you don’t feel the original equipment CCA specifications are appropriate in your area.

How you use the battery in your tow vehicle can also dictate the replacement battery you choose. For example, if you’ve added accessories such as auxiliary lights, a bigger stereo, a CB radio and a winch – and you use those items with the engine turned off – you can exceed the capacity of the stock battery and discharge it more than was intended.

In this case, you should seek a battery with maximum reserve capacity. This attribute, which often isn’t on the battery’s label, is the amount of minutes the battery will take to discharge with a 25-amp draw. For example, a 120-minute reserve capacity battery would be completely discharged after two hours, but could still possibly start the vehicle after one hour. The counterperson at your auto-parts store should be able to look up the reserve capacity of the battery (or batteries) you’re considering. Alternately, the technical-services department of a battery company can help you find a battery with adequate reserve capacity.

Technician Testing an RV Trailer battery

Technicians can check the battery reserve and diagnose any problems with an RV battery.

If you subject your battery (or batteries) to extraordinarily heavy-duty use, you may consider a battery that is physically larger, which can yield higher CCA, longer reserve capacity or both. However, this isn’t as easy as it sounds, because the engine compartments of today’s vehicles typically don’t have the room, and the battery tray is designed to accept a specific battery group. If you have the space for a bigger battery, or even dual batteries under extreme demand situations, by all means, go for it. Just remember that your stock charging system was designed for the stock battery, so the alternator and other components may require upgrading as well.

Batteries for the Trailer

For your trailer or camper, you’ll want a deep-cycle battery to power interior lights and other electrical components. Note that these batteries were not mentioned in the above section, and that is because they’re not intended for use as an automotive starting battery. An automotive battery is made to produce a high current for starting, while a deep-cycle battery is made to allow lower current for a longer period of time. Deep-cycle batteries don’t have as many CCA as starting batteries, and won’t provide as many starts.

However, where a starting battery might only survive 20-30 deep discharges, a deep-cycle battery can withstand repetitive discharges to a 50-percent depth of discharge or more and still continue to provide its rated capacity after hundreds of cycles. This characteristic, combined with more reserve capacity, makes deep-cycle batteries ideal for use in an RV application.

A deep-cycle battery differs from its automotive counterpart in its internal construction. There are typically fewer plates inside a deep-cycle battery than an automotive battery, but they are normally thicker and hold more lead-oxide paste, which chemically reacts with the sulfuric acid of the electrolyte. The paste itself is usually a higher density as well.

In your RV, reserve capacity is your primary consideration, and as with your tow vehicle, you can get more by going bigger and/or adding batteries. Many RVs come factory equipped with one battery, but they may have space for adding another. If a single battery suits your needs, you may choose only to go with a direct replacement, or upgrade to a physically larger battery if it fits. You’ll want batteries with the highest
amp/hour (ah) rating you can find; for example, a 100 ah battery is one that will produce 5 amps for 20 hours at 80° F before it reaches 1.75 volts per cell, or 10.5 volts.

RV Batteries Connected In Parallel to boost life.

Connecting batteries in parallel can ad life, but not voltage.

For those with more demanding power needs, adding 12-volt batteries and connecting them in parallel will double the amount of time before the batteries are discharged. If you go this route, you might as well opt for 6-volt, golf-cart batteries, which are connected in series to produce 12 volts. This setup can endure more deep discharges than a 12-volt marine/RV product (sometimes twice as many), which makes it popular with RVers who want the ability to operate their rigs through an inverter on battery power only.

If your trailer has multiple batteries, it’s important to consider them as individual components that comprise a single system. As such, it’s not a good idea to replace or upgrade only one battery; all of the batteries should be replaced with the same size and type. Placing a new battery in parallel with older/weaker batteries makes the new one work harder, and therefore will eventually make it as weak as the others.

When wiring the batteries, consider the following:
Parallel: Combines amps, not voltage.
Series: Combines voltage, not amperage.
Series/Parallel: When more than one pair of 6-volt batteries are connected
in a 12-volt system.

RV and Tow Vehicle Battery Maintenance

Checking an RV Battery with an voltage meter

The key to maintaining batteries is testing, testing, testing. A quick stop can save major hassles at the campsite.

Whether in your tow vehicle or in your RV, battery maintenance is key to long-lasting performance, although it’s typically not required as frequently as it once was. Though the vast majority of batteries in use today are still the flooded-cell variety, most of these are considered maintenance-free under normal conditions – even those with removable caps. However, it is still good practice to have the battery visually inspected and tested every few months.

If your battery requires water, it is preferred that you replenish it with distilled water. Also, make sure that the electrolyte (water) covers the plates inside by a minimum of 1/2-inch. If air contacts those plates for any length of time, it hardens the chemical paste material on the plates and causes them to sulfate. Once sulfation occurs, there is a pretty good chance that part of the plate is not going to be chemically use-able anymore. In other words, you may have lost a percentage of battery performance that you’re not going to get back.

Keeping your batteries charged is obviously important, but what may not be so obvious is how to keep them charged. Leaving an RV plugged in when not in use isn’t necessarily a good idea, as an overzealous charger can cook your batteries dry. A simple check is to plug the RV in for about a week; if the battery gets hot or loses water, it’s being overcharged and shouldn’t be left plugged in. Otherwise, you can leave it plugged in for a couple of weeks at a time, but a more reliable solution is to charge the batteries for a day or so once a month with a three-stage charger. This will keep them topped off without the danger of overcharging.

If you’ve removed the batteries from your tow vehicle or RV and want to recharge them, make sure you choose a battery charger that is compatible with the battery. It is best to recharge your batteries with a multi-stage charger, but here are some guidelines if you don’t have such a device: Divide the current (amp) level of battery amp/hours by five for fast charging, and divide by 10 for slower charging. Example: A 100 ah battery divided by five equals a 20-amp charger. Many battery chargers have an adjustable amp setting, which is handy for different battery types.

“Battery maintainers” are also a popular choice for keeping batteries topped off, but here again, make sure the one you choose is compatible with your battery or batteries. Prior to using the maintainer for an extended period of time, make sure the unit is providing the proper voltage, and fully charging the battery. After a few days, disconnect the maintainer for a couple of hours and then use a voltmeter or hydrometer to check the level of charge. A voltmeter should be about 12.6 volts, while a hydrometer should show a specific gravity number of 1.265, meaning the battery is at or near 100 percent charged.

After deep-cycle batteries have sat for several months without charging, or on a maintenance charge, they may require equalization. While this is a fairly involved topic unto itself, suffice it to say that “equalization” is a term meaning to de-sulfate or equalize individual cells of a battery. This is done through the use of a charger or converter that has the ability to charge at a high voltage (typically 15.6 to 16.2 volts) at a low current level in an attempt to break the sulfate crystals off the inner cell paste material.

Some battery manufacturers recommend equalization after 30-50 charge/ discharge cycles, while others don’t recommend equalization at all; check with your battery manufacturer to be sure. (Note: Battery equalization is for flooded-cell, deep-cycle batteries only – don’t attempt to equalize a gel-cell or absorbed-glass-mat battery without specific voltage requirements from the manufacturer.)

Last but not least, always make sure that your battery is properly secured, that the terminals are clean, and the connections are tight. An improperly secured battery can bang around on its tray, causing internal damage. Loose or dirty connections can cause starting/charging problems. If your terminals look like they’re growing their own culture, it’s time for a thorough cleaning. Disconnect the battery, then mix about one part
baking soda in four parts water, and pour it over the terminals. When the foaming subsides, rinse well with water and you’ll be amazed to find clean, gray terminals again. Mix another batch, and dip your connections, one at a time. When you’re done, rinse and dry everything off thoroughly, reconnect the terminals, and apply a small amount of die-electric grease to the connections to help retard oxidation. A little maintenance really does go a long way.

Apache Camping Center/Tacoma, Washington, (253) 535-6522, www.apachecamping.com.
Interstate Batteries, (800) CRANK IT, www.interstatebatteries.com.

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