Dear Dave,
My RV’s two 6-volt house batteries are dead and I was wondering if I could take the 12-volt battery out of my Jeep that I am going to store for a while and use it instead. Will it have enough power to operate the slides and the hydraulic stabilizers? The battery is only 9 months old and used on my 2002 Jeep Wrangler 4.0 TJ. Thanks. —Harry, 35-ft. 2000 Fleetwood Pace Arrow MH
Dear Harry,
Technically, yes, you can use the automotive 12-volt battery in your RV’s house system to replace the dead 6-volt batteries as they were connected in series, positive to negative, to create a 12-volt battery “bank.” However, your current batteries are “deep cycle,” meaning they are designed to be drawn down to 50% state of charge (SOC) and recharged repeatedly, which is the deep cycle.
Current batteries
The current batteries are designed to provide constant voltage for a long period of time, sometimes days, and are rated in amp hours (Ah) for how long they can provide 25 amps of power. Fleetwood has always been a fan of the 6-volt batteries and used them for years as they typically have more Ah ratings and provide more cycles. Since your rig is a 2000, I would assume your batteries are not original.
Automotive batteries
Automotive batteries are rating in cold cranking amps (CCA) and designed to provide a high amp power for 30 seconds to turn over an engine for starting purposes. They are not designed to provide power for a long period of time and do not liked to be drained and recharged or “cycled.” They will go dead fairly quickly if used in this application.
However, it depends on how you will be using your rig, meaning dry camping or being plugged into shoreline power. If you are dry camping and need to drain the battery and periodically recharge it, the automotive battery will not last long. However, if you are going to be plugged into shoreline power, the converter/charger of your rig will provide voltage to the battery and ultimately to the 12-volt system, depending on the type of charger you have.
If it is a typical converter/charger, it will provide a constant 13.2 volts, which will power everything and not do much damage to the automotive battery. If you have a converter that is designed to condition or desulfate the battery, like the older Progressive Dynamics models, it might provide a higher voltage charge in the range of 13.8 volts for eight hours. That might not be good for your automotive battery. If you have an inverter/charger like the green Freedom 2000 in the above photo, it could have a multi-stage charge that is also not a good charging profile.
Also, if you are going to be plugged in most of the time, you can leave the dead 6-volt batteries in the system and have the converter/charger provide constant power. However, it will sense the low SOC and run at a higher voltage—which could eventually ruin the converter.
Variables to consider
There are several variables to consider. I think either way you will need a new battery somewhere in the equation. If you use the automotive battery, most likely you will need a new one when you bring the Jeep out of storage. Or you buy a new 12-volt deep cycle battery for the rig up front and size it to the Ah you need for dry camping.
You might also enjoy these posts from Dave
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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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Hi Dave and Harry. I may have missed it but, I don’t remember reading anywhere “why” the house batteries were dead. Was is a parasitic drain, bad RV frame grounding, converter charging, or some other reason? It would be helpful to explore before replacing the batteries. There is a reason for this problem.
One other thing not mentioned is the terminals on the house batteries and auto battery are completely different.
The deep cycle batteries have a stud and nut. The auto battery uses a post and clamp.
Thank you for the DC power discussion, Dave! In particular, thank you for the discussion of the differences between an automotive battery and a deep-cycle battery. Have a great day and safe travels!
You nailed it Dave.
To visualize the difference in batteries is to think about how a car dome light left on will drain the car’s battery by morning yet a deep cycle battery of the same voltage will go much, much longer under the same load.