July 6, 2021

TT# 125 12 Volt RV Battery and Control Systems, Care and More! (Part 6)

By: Rob Lowe

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This TechTip is the last of a series of six, that covers the twelve-volt (12V) battery and power systems used in modern RVs.  All RVs depend upon a reliable twelve-volt (12V) power source, however that venerable 12-volt system has been changing under the ever-increasing demands being placed on it. These TechTips will focus on the power sources that are found in a motorhome consisting of two independent 12V systems, one for the engine and the ‘on-the-road’ systems and the second for the ‘Coach’ or ‘house control’ system. Unlike motorhomes, trailers have a single Coach power system, lacking the complexity of having two independent co-existing systems.
The Topics covered in this group of TechTips are:
The impact of the use of Computerized Control (Multiplex) Systems (TechTip #120)
Battery Types and the Significance of Battery Type on usability (TechTip #121) 
Inverter/Charger systems and settings (TechTip #122)
New products that Improve Battery Longevity and Maintenance (TechTip #123) 
The interaction between Chassis and Coach Battery Systems (TechTip #124)
An Alternative Battery Maintenance Approach while a Coach is in Storage (TechTip #125) (This one)

Questions arise from a lack of understanding about how these systems operate, as expressed by new owners, as well as recent significant changes in the systems themselves, often overlooked by experienced RVers as they exchange their RV. This TechTip series will assist both in understanding the battery, the control and inverter systems. 

Since motorhomes have two battery systems, it is important that both systems charge when the coach is being driven as well as when the coach is parked at a campground and connected to a Coach power source. Of course, newer RVs often have a solar charging system that can assist with the charging when the RV is in direct sunshine.

Battery Charging While a Coach is Not in Use: (in Storage, as an example)
Rather than rewrite an article that I first published on my Blog on October 22,2015; I have updated the article in this TechTip. It will cap off this series of articles on RV Batteries and Control Systems. I write blog articles to cover topics that often do not warrant a complete detailed TechTip, yet they address topics that are raised in conversations, email exchanges or arise out of an issue that an RVer has experienced. When you have time, I recommend that you go to my website, click on the Blog tab from the landing Home page and review the Blog- Rob’s Blog articles to learn a lot about your RV and perhaps answer your questions.

Here is the updated Blog article:

A question, RVers frequently ask in the fall when planning to store their coaches for a longer periods of time (such as over the winter) is: What is the best way to store my RV’s batteries?
The traditional answer has been that it is always best to remove them, store them inside on a wood surface and periodically charge them.  This avoids the need to have 120 Volt AC (120VAC) power available in the RV’s winter storage location, especially if the coach has a 50 or 30 Amp. power cord that the storage facility does not have. It also makes routine checking and charging of the batteries easier, since often the batteries are stored at home. If a battery freezes in the RV, it will likely crack, leaking sulfuric acid, ruining the battery and damaging the floor of the battery compartment. Part of the challenge of removing batteries, is physically removing multiple, heavy, lead-Acid batteries, noting the exact way the wiring is connected, then reversing the procedure and re-connecting the battery wiring correctly when reinstalling them. This is especially true when one looks at the various battery configurations RV makers are using. Note: It is important even after removing the batteries, to periodically charge them to ensure they are kept in top condition. More information on this follows. 

What is the second best alternative? If there is dependable 120VAC available at the RV storage location, then leaving them in the RV is a possibility. Ensure that the batteries are fully charged (and in good condition), with the fluid at the proper level and that all connections are clean and tight. Battery disconnects should all be turned off (to disconnect the batteries) when the RV is not in use. This is especially important during winter or seasonal storage. Even with the disconnects turned off, there are still numerous things receiving DC power. Parasitic loads, (as these are referred to), include electronic items such as the radio, clock and control system memories, in addition to engine and transmission computers memories among other items. During the RV season, the batteries would be able to maintain a suitable charge level, if left disconnected for 30 days.  This timeframe decreases rapidly at winter temperatures since the chemical activity of the battery decreases as the temperature falls. Newer RVs have the option to add solar panels with solar controls, often in the 100 to 300 watts range, which will maintain a connected battery system provided the storage location has adequate sunlight. The challenge is that these systems rarely are connected to more than one battery system (often the Coach, not the Chassis). 

Seasonal Storage of Batteries left in RV (Charging using the RV Power Cord)  
Even though you may have 120VAC available, I do not recommend leaving the converter or inverter/charger powered all winter, by simply plugging the RV power cord into a 30Amp or 50Amp power outlet. Many modern electronic items in the coach have an ‘instant on’ function, use 120VAC are also on, drawing power. These include all modern TVs, DVD systems, satellite receivers among others. Not only is this approach a waste of electricity, by powering them all the time, the components age prematurely, even when they are not being ‘used’. Another factor is that in some RVs, turning off the Battery Disconnects, (often done when a RV is stored), removes the charging current from the battery. Some may choose to leave the batteries connected, and plugged in. While this is a possible solution, how well this works depends upon the control system that operates the charger. Some RVers have discovered the hard way, that when a battery begins to fail, it may cause the charging system to feed power to the low (failing) battery only, leaving another set of batteries without any charging power. These uncharged or low batteries may freeze in cold climates, which will shorten their life and require premature replacement of not only the original defective battery, but often one or more other batteries.  

Another Solution to Battery Charging While a Coach is Not in Use (as in Storage)
Charging Alternative While in StorageI have studied this problem and concluded that there is a simple solution that works very well. I have used either two-single (See photos) or one-double circuit Deltran Battery Tender® Battery Maintainer (www.batterytender.com) on my RVs, car and motorcycles for over ten (10) years. If the Coach and Chassis batteries are in the same area, then one circuit of the Bank Charger (Two Circuit) version, can be directly connected to the Coach battery system and the other circuit to the Chassis battery.  (See photo showing batteries) If the batteries are in different areas of the RV, you can choose to install one Maintainer near each battery. Alternatively, I have used two independent Deltran Battery Tender® Battery Maintainers, installed where the Battery Control Center is found on the coach. Even though the batteries are in different locations, the wiring from each battery comes to the Battery Control Center. That connection and a ground connection is all that is needed to make the RV ready to maintain each battery system.  See the enclosed Photos for installations of both versions. 

Two Battery Maintainers off 1 CordThese maintainers have one or two sets of polarized connectors that can be permanently connected to each set of batteries or using the included set(s) of battery cables that can be clipped to the battery posts and removed when not needed. Each connection is then capped for safety. When the RV is going into storage, the mating connectors on each maintainer is connected to those on each battery and connected to a reliable source of 120VAC power. (See Green Arrows)
They are designed to keep fully charged batteries (without excessive loads on them), charged for long periods when the RV is not used. All of these are low current Battery Maintainers not higher current Battery Chargers. That is, the unit monitors the battery voltage of each system and, if required, cycles on a low current maintenance charge as needed when signaled by the monitored battery’s voltage, then it cycles off as the battery returns to a fully charged state. Every one of these Battery Maintainers can be powered with a light duty regular extension cord run to the location where the unit is mounted (close to or in the battery compartment). (Red Arrow) The green or red lights on the smaller Tenders (green light reflected on left in photos) or a sequence of charging bars and lights tell you what phase the maintainer is in and whether the batteries are fully charged or not. 


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