I have room for One 12V Battery on my trailer ...

... what should it be?  The group 24 (Napa) that came with the trailer (new last year) only lasts barely two days dry camping.  We're weekend campers, taking off on a Thursday or Friday and camping for 2 or 3 days.  Seems like every time we go, we end up at a beautiful campground with no electricity.  All we run are the lights and the water pump, maybe the furnace for a bit in the morning (couldn't get the slide back in without charging the battery with the car).  I was thinking of buying a new battery; group 31 will fit.  My question is, how much difference will it make?  Will I get one more day out of it?  During the summer, I'm keeping the trailer in the driveway, plugged into shore power.  We're leaving tomorrow for a two-dayer on the Oregon Coast.  I'm trying to lessen the battery worry for this trip.

And ... if I buy one, I can choose from Sears, Walmart, Costco, or the local Batteries Plus.  Where would you go?

Wherever you buy the battery, be sure it's a true deep cycle battery.  Not a starting battery or a marine battery.

Like Ned said, get the biggest, true deep cycle battery that will fit.  Being a dry camper, you really should have two deep cycle batteries in parallel if the running of the furnace is involved.  The furnace blower is a power hog.  Maybe warmer bedding would save a bit on the battery you chose if it gets cold enough at night where you are thinking of firing up the furnace.  I choose cuddling.  But that's just me. 

Also, if you prefer boondocking, switching your interior lighting to LEDs will save a bunch of strain on whatever  battery you choose.  Something to think about.  Lots of info here in the forum library about the subject.  Discount available for members.

If you are just a weekender as implied,  you won't be sorry to have a little extra power available by having two batteries.  If you have the room for two.  If no room for two, the biggest true deep cycle you can possibly fit in the space is what you need.  As well as careful management on power usage in between recharges. 

The thing you're looking for is amp hours, the amount of energy stored in the battery. As you battery shop you are looking for a 12v deep cycle battery with the most amount of amp hours in it, typically calculated at the 20 hour rate. You aren't looking for Cold Cranking Amps which is important for a starting battery. Most deep cycle will be between 80 and 105 AH. You want to buy the 105.

Measure your battery box and get the biggest battery/most amp hours possible. If you've got an 80 AH battery now, going to 105 AH will be a 25% increase in battery life! This battery http://www.batteriesplus.com/product/33840-SLI31MDC-Xtreme-Deep-Cycle-Battery/100079-1/102530-Marine-and-Boat-Batteries/106979-Deep-Cycle/BCI-Group-31M.aspx looks like what I'd buy if I was constrained by size and could only fit one 31 series battery in my rig. At 59 pounds is has a pretty good amount of lead in it which is also a good indicator of battery capacity.

Ken

Thanks, everybody.  I picked up a Diehard Model # 27582, group 29.  Installed it this afternoon, and am getting it fully charged before we take off tomorrow.  This is the biggest one that would fit on the tongue due to the placement of the weight distribution hitch clamps where the chains hook up.  Anyway, the only snafu was the fact that the propane hose was so short and tight up against the old battery box that I had to go buy a longer propane hose for more slack.  Oh well, another "but first" project in my world is no big surprise!

I'll let you know how the weekend goes.  I was not able to replace all my bulbs with leds, but bought a very nice led lantern at Costco that we'll use at night instead of the on-board lighting that may be drawing extra amps.  Also, I plan to remove the fuse for the stereo in there as the light stays on even though we're not using it and maybe that's part of our problem. 

Have a great weekend!

You should do well. A Group 29 size deep cycle battery has almost 40% greater amp-hour capacity than a Group 24. The Diehard #27582 has an AH rating of 115, whereas your previous size 24 would have been 85 at most.  It's a marine type battery, so I would not expect as long a useful life as a true deep cycle, but while it lasts it should perform well.

So, if it says Deep Cycle (like the one I just bought), it may not be a true deep cycle?  It's so confusing ... what's the difference?

"Marine" on the label is the telltale. A  marine battery is a hybrid between automotive and pure deep cycle, but far more automotive than it is deep cycle. It is designed to crank marine engines and also provide auxiliary power, whereas a pure deep cycle makes no attempt at engine cranking capability. That design difference enables it to use a different type of internal design that will typically last for 7+ years as an RV house battery.

The marine battery is internally very similar to an automotive engine starting battery and can be built on the same assembly line, thus taking advantage of its economy of scale and reducing the price substantially.

I did say to not get a marine battery.

1kwords said:

So, if it says Deep Cycle (like the one I just bought), it may not be a true deep cycle?  It's so confusing ... what's the difference?

Click to expand...

The difference is the constructions inside. An automotive battery has many thin plates to give Cranking Amperage to the system. More thin plates give more surface area which allows a large supply of energy all at once.

A true deep cycle battery has fewer but thicker plates inside. Remember I talked about more lead and heavier weight before? These batteries allow smaller loads but for a longer time. Nothing in your rig uses a large amount of electricity at one time like the starter on your car/truck, so this design is perfect for smaller, longer draws of energy.

As a battery charges and discharges small particles of the lead plates flake off. The thick plates of the true deep cycle are designed to allow this to happen for a large number of cycles. The thinner plates of an automotive battery are not designed to be deeply discharged, and will fail if deeply discharged many times. The further down towards dead the battery is discharged the more of these particles flake off. This is why it is recommended to not draw a battery more than halfway dead.

A "marine" or "marine/RV" battery is a battery with a construction in between the automotive and the deep cycle. It will not allow as many discharge/charge cycles as a true deep cycle and it won't give as big a burst of energy in starting situations.

However, having said all that very few people take good enough care of their batteries to get the optimum life possible anyway. Many people draw their batteries below a half discharge, they don't water them properly, and they don't pay attention to charging the battery and keeping it topped off properly.

Your specific problem, size of space available for the battery and the battery types readily available that fit in that space may make the marine/RV battery a reasonable choice for you. The AH rating is probably as much as you could expect. Paying attention to the maintenance and charging of your battery should give you a reasonable service life. Each of us uses our equipment just a little differently, and we all have to find what works best for us. If this battery provides power for the 3 days you need and you get a reasonable service life, then you've found what you need.

Ken

Thank you so much, Ken, for the time it took you to explain all of that.  I really appreciate it.  When I went into Sears, all they had for deep cycle batteries were Marine batteries, and the sales person was someone who has a trailer, too, and recommended this battery.  And you're right; we all have different ways of how we use our trailers and how we take care of the parts that go into it.  For us, I think this battery will be fine.  Since we are only weekenders (aside from a week long trip in August to Coeur d'Lene which will include electrical sites), my method of care of this battery will most likely be plugging into the house when we get back to keep it charged.  For longer times it sits idle, I'll use the battery tender. 

Thanks again for the explanation!  This forum is so helpful.

Note that the differences between automotive starting battery construction and deep cycle construction has to do with longevity moreso than capacity.  The initial AH or RC rating on the two types will typically be identical, but after a season of use in an RV, the true deep cycle will likely be good as new, whereas the starting battery is probably already suffering a loss of capacity. But it really does depend on just how it is used.