Battery Dies When my RV is stored
Dave and Helen Damouth www.damouth.com
revised January 20, 2000
Q: When parked empty for a few days (stored) the battery lasts about 3 days. The only power draw is the propane detector.
It's unlikely that the propane detector is the *only* power draw. Most rigs will have additional "phantom" power drains that you can't normally shut off.
As others have pointed out, most refrigerators will have a small 12v. power drain when running on propane. Newer refrigerators with automatic switchover between propane and shore power have more electronics and a somewhat larger power draw while on propane. Many refrigerators have a hidden "high humidity" switch which turns on a heater around the door gaskets - drawing quite a bit of power. Make sure this is off. I once found that the light in my refrigerator was not turning off when the door was closed (misadjusted door or switch).
The displays on microwave and radio/stereo probably stay on (and draw power) all the time - perhaps showing the time. Many tv's draw some power even when turned off. And so on. Even with all these things accounted for, my trailer has about 0.1 amp of mysterious power drain that I've never been able to locate.
Q: Everything else is off. The detector book says it draws .185 amps/hour. Does that seem like it is enough to draw down a fully charged battery?
0.185 amps times 24 hours times 3 days = 13 amphours. Guessing from your description, below, your battery may be a low priced medium-to-low quality group 24 "dual purpose" product, and when new, fully charged, is probably rated for around 75 amphours, which means the battery should run your propane detector for up to 16 days, if there is no other drain.
But my trailer, before I systematically located and disabled all the "phantom" power drains, had a continuous drain of something like 0.8 amps with "everything turned off". If yours is similar, and if your battery isn't new, then a 3-day battery life is not surprising.
Q: A side issue is how many amps does a typical RV battery provide. We have the smaller 12 volt battery. (550 cold cranking amps I think) How many real amps is there in a CCA.
If your battery has a CCA rating, then it is not well suited for use as an RV house battery. Rather, it is designed for engine-starting applications, which requires quite a different battery design.
From your comments, it sounds like you may have let your battery fully discharge on several occasions. This damages any battery, and particularly an engine starting battery - permanently reducing the total storage capacity. If you want to retain the battery's original storage capacity for a long time (years), then the battery should never be discharged all the way. It is generally recommended that the battery not be routinely discharged more than half of its capacity.
In choosing an RV house battery, you should look for a battery specifically designed for deep-discharge use. It should have an amphour rating, or lacking that, at least a "reserve capacity" rating. You can roughly convert reserve capacity to amphours by multiplying by 0.65. If the battery also has a CCA rating, or perhaps the newer "MCA" rating (for marine applications), avoid it - it is a compromise dual-purpose battery and will not perform as well as a true deep-cycle battery.
Good 12-volt deep-cycle batteries are available in group 24 and 27 sizes. You may have to buy them at large specialty RV or Marine stores, and thus will pay a premium price. West Marine, for example, has group 24 for $88 and group 27 for $90. Their group 24 is rated at 85 ah and the group 27 is rated at 105 ah. They also have an even larger group 30H for $111, rated at 130 ah. Note that the group 24 is a very poor choice - much less capacity than the group 27, at about the same price.
This same store will sell you a dual-purpose group 24 battery for $60 and a group 24 engine starting battery for as low as $40. The latter probably has an effective amphour capacity of only 40 ah - half the capacity of the group 24 deep-cycle battery. More importantly, when used as a house battery, it will probably have a lifetime of perhaps 1/3 of the deep cycle battery. You'd be lucky if it lasted one season. The more expensive deep-cycle battery is a *much* better buy. The bigger group 27 is also a *much* better buy than the 24. As mentioned previously, the dual-purpose battery is somewhere in the middle - a compromise - hence a bad idea unless you really need to both start a small engine and run your RV lights from the same battery (which is typical in a small boat but very unusual in an RV.)
Q: I have thought about putting a switch on the detector to turn it off when not being used.
Having read this far, you'll have realized that turning the detector off probably won't solve your problem. You have several options
First, as others have suggested, you could install a battery disconnect switch. These are readily available in RV, marine, or auto parts stores. The simplest to install are mounted directly on a battery terminal. Once you've disconnected *everything* from the battery, it will still discharge from internal leakage, but if the battery is in good condition, you can safely leave it for up to a month or so in summer, longer in cold weather. Installing this switch is a good idea even if you also do one of the following.
Second, you can buy a small multi-stage battery charger, and leave it plugged in while the trailer is in storage. This will safely keep your battery fully charged. This would let you leave your refrigerator, propane detector, etc, running for a week or two between trips - a real convenience.
Third, (cheaper but less convenient) you can buy a real cheap trickle charger and a timer. You set the timer to run the trickle charger for a short period each day, and this will top off the battery without damage. How long you run the charger depends on just how big your "phantom" power draw really is and what the actual current output of the trickle charger is. Start fairly short (perhaps an hour) and measure the battery charge (with an inexpensive hydrometer *not* a voltmeter) after a few days. If the battery charge level is drifting downward, increase the time a little. If the battery is noticeably bubbling or losing water, reduce the time. With experience, you'll learn the right timer setting.
Fourth (most convenient but most expensive), you can replace your existing converter/charger with a modern one that has a multi-stage charger. These have the advantage of charging quickly when needed, at high current, but automatically sense when the battery is fully charged and then back off to a tiny maintenance charge rate. With this "smart" charger, you can just leave your rig plugged in year-around and don't worry about the battery.